diff --git a/library/Icinga/Application/Config.php b/library/Icinga/Application/Config.php
index a6bcb8c66..006c40fbc 100644
--- a/library/Icinga/Application/Config.php
+++ b/library/Icinga/Application/Config.php
@@ -122,7 +122,7 @@ class Config implements Countable, Iterator, Selectable
      *
      * @return  int
      */
-    public function count()
+    public function count(): int
     {
         return $this->select()->count();
     }
@@ -130,11 +130,11 @@ class Config implements Countable, Iterator, Selectable
     /**
      * Reset the current position of the internal config object
      *
-     * @return  ConfigObject
+     * @return  void
      */
-    public function rewind()
+    public function rewind(): void
     {
-        return $this->config->rewind();
+        $this->config->rewind();
     }
 
     /**
@@ -142,7 +142,7 @@ class Config implements Countable, Iterator, Selectable
      *
      * @return  ConfigObject
      */
-    public function current()
+    public function current(): ConfigObject
     {
         return $this->config->current();
     }
@@ -152,7 +152,7 @@ class Config implements Countable, Iterator, Selectable
      *
      * @return  bool
      */
-    public function valid()
+    public function valid(): bool
     {
         return $this->config->valid();
     }
@@ -162,7 +162,7 @@ class Config implements Countable, Iterator, Selectable
      *
      * @return  string
      */
-    public function key()
+    public function key(): string
     {
         return $this->config->key();
     }
@@ -170,11 +170,11 @@ class Config implements Countable, Iterator, Selectable
     /**
      * Advance the position of the current iteration and return the new section
      *
-     * @return  ConfigObject
+     * @return  void
      */
-    public function next()
+    public function next(): void
     {
-        return $this->config->next();
+        $this->config->next();
     }
 
     /**
diff --git a/library/Icinga/Application/Hook/Ticket/TicketPattern.php b/library/Icinga/Application/Hook/Ticket/TicketPattern.php
index 8116ca6be..e37fcc1f8 100644
--- a/library/Icinga/Application/Hook/Ticket/TicketPattern.php
+++ b/library/Icinga/Application/Hook/Ticket/TicketPattern.php
@@ -34,26 +34,17 @@ class TicketPattern implements ArrayAccess
      */
     protected $pattern;
 
-    /**
-     * {@inheritdoc}
-     */
-    public function offsetExists($offset)
+    public function offsetExists($offset): bool
     {
         return isset($this->match[$offset]);
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function offsetGet($offset)
+    public function offsetGet($offset): ?string
     {
         return array_key_exists($offset, $this->match) ? $this->match[$offset] : null;
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function offsetSet($offset, $value)
+    public function offsetSet($offset, $value): void
     {
         if ($offset === null) {
             $this->match[] = $value;
@@ -62,10 +53,7 @@ class TicketPattern implements ArrayAccess
         }
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function offsetUnset($offset)
+    public function offsetUnset($offset): void
     {
         unset($this->match[$offset]);
     }
diff --git a/library/Icinga/Application/Libraries.php b/library/Icinga/Application/Libraries.php
index f250210f8..63662fde9 100644
--- a/library/Icinga/Application/Libraries.php
+++ b/library/Icinga/Application/Libraries.php
@@ -6,6 +6,7 @@ namespace Icinga\Application;
 use ArrayIterator;
 use IteratorAggregate;
 use Icinga\Application\Libraries\Library;
+use Traversable;
 
 class Libraries implements IteratorAggregate
 {
@@ -17,7 +18,7 @@ class Libraries implements IteratorAggregate
      *
      * @return ArrayIterator
      */
-    public function getIterator()
+    public function getIterator(): Traversable
     {
         return new ArrayIterator($this->libraries);
     }
diff --git a/library/Icinga/Authentication/AuthChain.php b/library/Icinga/Authentication/AuthChain.php
index cdae75adb..39468e3cf 100644
--- a/library/Icinga/Authentication/AuthChain.php
+++ b/library/Icinga/Authentication/AuthChain.php
@@ -184,12 +184,12 @@ class AuthChain implements Authenticatable, Iterator
     /**
      * Rewind the chain
      *
-     * @return ConfigObject
+     * @return void
      */
-    public function rewind()
+    public function rewind(): void
     {
         $this->currentBackend = null;
-        return $this->config->rewind();
+        $this->config->rewind();
     }
 
     /**
@@ -197,7 +197,7 @@ class AuthChain implements Authenticatable, Iterator
      *
      * @return UserBackendInterface
      */
-    public function current()
+    public function current(): UserBackendInterface
     {
         return $this->currentBackend;
     }
@@ -207,7 +207,7 @@ class AuthChain implements Authenticatable, Iterator
      *
      * @return string
      */
-    public function key()
+    public function key(): string
     {
         return $this->config->key();
     }
@@ -215,11 +215,11 @@ class AuthChain implements Authenticatable, Iterator
     /**
      * Move forward to the next user backend config
      *
-     * @return ConfigObject
+     * @return void
      */
-    public function next()
+    public function next(): void
     {
-        return $this->config->next();
+        $this->config->next();
     }
 
     /**
@@ -228,7 +228,7 @@ class AuthChain implements Authenticatable, Iterator
      *
      * @return bool
      */
-    public function valid()
+    public function valid(): bool
     {
         if (! $this->config->valid()) {
             // Stop when there are no more backends to check
diff --git a/library/Icinga/Data/ConfigObject.php b/library/Icinga/Data/ConfigObject.php
index 1cbc6873a..2ab5522ab 100644
--- a/library/Icinga/Data/ConfigObject.php
+++ b/library/Icinga/Data/ConfigObject.php
@@ -50,11 +50,11 @@ class ConfigObject extends ArrayDatasource implements Iterator, ArrayAccess
     /**
      * Reset the current position of $this->data
      *
-     * @return  mixed
+     * @return  void
      */
-    public function rewind()
+    public function rewind(): void
     {
-        return reset($this->data);
+        reset($this->data);
     }
 
     /**
@@ -62,6 +62,7 @@ class ConfigObject extends ArrayDatasource implements Iterator, ArrayAccess
      *
      * @return  mixed
      */
+    #[\ReturnTypeWillChange]
     public function current()
     {
         return current($this->data);
@@ -72,7 +73,7 @@ class ConfigObject extends ArrayDatasource implements Iterator, ArrayAccess
      *
      * @return  bool
      */
-    public function valid()
+    public function valid(): bool
     {
         return key($this->data) !== null;
     }
@@ -80,9 +81,9 @@ class ConfigObject extends ArrayDatasource implements Iterator, ArrayAccess
     /**
      * Return the section's or property's name of the current iteration
      *
-     * @return  mixed
+     * @return  string
      */
-    public function key()
+    public function key(): string
     {
         return key($this->data);
     }
@@ -90,11 +91,11 @@ class ConfigObject extends ArrayDatasource implements Iterator, ArrayAccess
     /**
      * Advance the position of the current iteration and return the new section's or property's value
      *
-     * @return  mixed
+     * @return  void
      */
-    public function next()
+    public function next(): void
     {
-        return next($this->data);
+        next($this->data);
     }
 
     /**
@@ -153,7 +154,7 @@ class ConfigObject extends ArrayDatasource implements Iterator, ArrayAccess
      *
      * @return  bool
      */
-    public function offsetExists($key)
+    public function offsetExists($key): bool
     {
         return isset($this->$key);
     }
@@ -163,8 +164,9 @@ class ConfigObject extends ArrayDatasource implements Iterator, ArrayAccess
      *
      * @param   string  $key    The name of the property or section
      *
-     * @return  mixed|NULL      The value or NULL in case $key does not exist
+     * @return  ?mixed      The value or NULL in case $key does not exist
      */
+    #[\ReturnTypeWillChange]
     public function offsetGet($key)
     {
         return $this->get($key);
@@ -178,7 +180,7 @@ class ConfigObject extends ArrayDatasource implements Iterator, ArrayAccess
      *
      * @throws  ProgrammingError    If the key is null
      */
-    public function offsetSet($key, $value)
+    public function offsetSet($key, $value): void
     {
         if ($key === null) {
             throw new ProgrammingError('Appending values without an explicit key is not supported');
@@ -192,7 +194,7 @@ class ConfigObject extends ArrayDatasource implements Iterator, ArrayAccess
      *
      * @param   string  $key    The property or section to remove
      */
-    public function offsetUnset($key)
+    public function offsetUnset($key): void
     {
         unset($this->$key);
     }
diff --git a/library/Icinga/Data/Db/DbQuery.php b/library/Icinga/Data/Db/DbQuery.php
index 8b3ee082d..457308093 100644
--- a/library/Icinga/Data/Db/DbQuery.php
+++ b/library/Icinga/Data/Db/DbQuery.php
@@ -410,7 +410,7 @@ class DbQuery extends SimpleQuery
      *
      * @return int
      */
-    public function count()
+    public function count(): int
     {
         if ($this->count === null) {
             $this->count = parent::count();
diff --git a/library/Icinga/Data/SimpleQuery.php b/library/Icinga/Data/SimpleQuery.php
index e4b9f1f9b..7e854eb64 100644
--- a/library/Icinga/Data/SimpleQuery.php
+++ b/library/Icinga/Data/SimpleQuery.php
@@ -165,7 +165,7 @@ class SimpleQuery implements QueryInterface, Queryable, Iterator
     /**
      * Start or rewind the iteration
      */
-    public function rewind()
+    public function rewind(): void
     {
         if ($this->iterator === null) {
             $iterator = $this->ds->query($this);
@@ -184,8 +184,9 @@ class SimpleQuery implements QueryInterface, Queryable, Iterator
     /**
      * Fetch and return the current row of this query's result
      *
-     * @return  object
+     * @return  mixed
      */
+    #[\ReturnTypeWillChange]
     public function current()
     {
         return $this->iterator->current();
@@ -196,7 +197,7 @@ class SimpleQuery implements QueryInterface, Queryable, Iterator
      *
      * @return  bool
      */
-    public function valid()
+    public function valid(): bool
     {
         $valid = $this->iterator->valid();
         if ($valid && $this->peekAhead && $this->hasLimit() && $this->iteratorPosition + 1 === $this->getLimit()) {
@@ -221,6 +222,7 @@ class SimpleQuery implements QueryInterface, Queryable, Iterator
      *
      * @return  mixed
      */
+    #[\ReturnTypeWillChange]
     public function key()
     {
         return $this->iterator->key();
@@ -229,7 +231,7 @@ class SimpleQuery implements QueryInterface, Queryable, Iterator
     /**
      * Advance to the next row of this query's result
      */
-    public function next()
+    public function next(): void
     {
         $this->iterator->next();
         $this->iteratorPosition += 1;
@@ -648,7 +650,7 @@ class SimpleQuery implements QueryInterface, Queryable, Iterator
      *
      * @return  int
      */
-    public function count()
+    public function count(): int
     {
         $query = clone $this;
         $query->limit(0, 0);
diff --git a/library/Icinga/Data/Tree/SimpleTree.php b/library/Icinga/Data/Tree/SimpleTree.php
index d4ffc1567..e89f58929 100644
--- a/library/Icinga/Data/Tree/SimpleTree.php
+++ b/library/Icinga/Data/Tree/SimpleTree.php
@@ -5,6 +5,7 @@ namespace Icinga\Data\Tree;
 
 use IteratorAggregate;
 use LogicException;
+use Traversable;
 
 /**
  * A simple tree
@@ -80,10 +81,9 @@ class SimpleTree implements IteratorAggregate
     }
 
     /**
-     * {@inheritdoc}
      * @return TreeNodeIterator
      */
-    public function getIterator()
+    public function getIterator(): Traversable
     {
         return new TreeNodeIterator($this->sentinel);
     }
diff --git a/library/Icinga/Data/Tree/TreeNodeIterator.php b/library/Icinga/Data/Tree/TreeNodeIterator.php
index 839b1a1d0..cffc9f451 100644
--- a/library/Icinga/Data/Tree/TreeNodeIterator.php
+++ b/library/Icinga/Data/Tree/TreeNodeIterator.php
@@ -28,59 +28,37 @@ class TreeNodeIterator implements RecursiveIterator
         $this->children = new ArrayIterator($node->getChildren());
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function current()
+    public function current(): TreeNode
     {
         return $this->children->current();
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function key()
+    public function key(): int
     {
         return $this->children->key();
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function next()
+    public function next(): void
     {
         $this->children->next();
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function rewind()
+    public function rewind(): void
     {
         $this->children->rewind();
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function valid()
+    public function valid(): bool
     {
         return $this->children->valid();
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function hasChildren()
+    public function hasChildren(): bool
     {
         return $this->current()->hasChildren();
     }
 
-    /**
-     * {@inheritdoc}
-     * @return TreeNodeIterator
-     */
-    public function getChildren()
+    public function getChildren(): TreeNodeIterator
     {
         return new static($this->current());
     }
diff --git a/library/Icinga/File/Storage/LocalFileStorage.php b/library/Icinga/File/Storage/LocalFileStorage.php
index e3ed5d679..e38167e5a 100644
--- a/library/Icinga/File/Storage/LocalFileStorage.php
+++ b/library/Icinga/File/Storage/LocalFileStorage.php
@@ -11,6 +11,7 @@ use Icinga\Exception\NotWritableError;
 use InvalidArgumentException;
 use RecursiveDirectoryIterator;
 use RecursiveIteratorIterator;
+use Traversable;
 use UnexpectedValueException;
 
 /**
@@ -35,7 +36,7 @@ class LocalFileStorage implements StorageInterface
         $this->baseDir = rtrim($baseDir, DIRECTORY_SEPARATOR);
     }
 
-    public function getIterator()
+    public function getIterator(): Traversable
     {
         try {
             return new RecursiveIteratorIterator(
diff --git a/library/Icinga/File/Storage/StorageInterface.php b/library/Icinga/File/Storage/StorageInterface.php
index cdcec777a..f416b009d 100644
--- a/library/Icinga/File/Storage/StorageInterface.php
+++ b/library/Icinga/File/Storage/StorageInterface.php
@@ -19,7 +19,7 @@ interface StorageInterface extends IteratorAggregate
      *
      * @throws  NotReadableError    If the file list can't be read
      */
-    public function getIterator();
+    public function getIterator(): Traversable;
 
     /**
      * Return whether the given file exists
diff --git a/library/Icinga/Protocol/File/FileIterator.php b/library/Icinga/Protocol/File/FileIterator.php
index b43b76075..64b66008c 100644
--- a/library/Icinga/Protocol/File/FileIterator.php
+++ b/library/Icinga/Protocol/File/FileIterator.php
@@ -44,7 +44,7 @@ class FileIterator extends EnumeratingFilterIterator
      *
      * @return array
      */
-    public function current()
+    public function current(): array
     {
         return $this->currentData;
     }
@@ -56,7 +56,7 @@ class FileIterator extends EnumeratingFilterIterator
      *
      * @throws FileReaderException  If PHP failed parsing the PCRE pattern
      */
-    public function accept()
+    public function accept(): bool
     {
         $data = array();
         $matched = preg_match(
diff --git a/library/Icinga/Protocol/File/FileReader.php b/library/Icinga/Protocol/File/FileReader.php
index da6bb2886..d16038741 100644
--- a/library/Icinga/Protocol/File/FileReader.php
+++ b/library/Icinga/Protocol/File/FileReader.php
@@ -89,7 +89,7 @@ class FileReader implements Selectable, Countable
      *
      * @return int
      */
-    public function count()
+    public function count(): int
     {
         if ($this->count === null) {
             $this->count = iterator_count($this->iterate());
diff --git a/library/Icinga/Protocol/File/LogFileIterator.php b/library/Icinga/Protocol/File/LogFileIterator.php
index 61cfc35cc..67a4d99d1 100644
--- a/library/Icinga/Protocol/File/LogFileIterator.php
+++ b/library/Icinga/Protocol/File/LogFileIterator.php
@@ -30,7 +30,7 @@ class LogFileIterator implements Iterator
     /**
      * Value for static::current()
      *
-     * @var string
+     * @var array
      */
     protected $current;
 
@@ -68,40 +68,31 @@ class LogFileIterator implements Iterator
         $this->fields = $fields;
     }
 
-    public function rewind()
+    public function rewind(): void
     {
         $this->file->rewind();
         $this->index = 0;
         $this->nextMessage();
     }
 
-    public function next()
+    public function next(): void
     {
         $this->file->next();
         ++$this->index;
         $this->nextMessage();
     }
 
-    /**
-     * @return string
-     */
-    public function current()
+    public function current(): array
     {
         return $this->current;
     }
 
-    /**
-     * @return int
-     */
-    public function key()
+    public function key(): int
     {
         return $this->index;
     }
 
-    /**
-     * @return boolean
-     */
-    public function valid()
+    public function valid(): bool
     {
         return $this->valid;
     }
diff --git a/library/Icinga/Repository/RepositoryQuery.php b/library/Icinga/Repository/RepositoryQuery.php
index 6e4297180..31395324c 100644
--- a/library/Icinga/Repository/RepositoryQuery.php
+++ b/library/Icinga/Repository/RepositoryQuery.php
@@ -690,7 +690,7 @@ class RepositoryQuery implements QueryInterface, SortRules, FilterColumns, Itera
      *
      * @return  int
      */
-    public function count()
+    public function count(): int
     {
         return $this->query->count();
     }
@@ -708,7 +708,7 @@ class RepositoryQuery implements QueryInterface, SortRules, FilterColumns, Itera
     /**
      * Start or rewind the iteration
      */
-    public function rewind()
+    public function rewind(): void
     {
         if ($this->iterator === null) {
             if (! $this->hasOrder()) {
@@ -735,8 +735,9 @@ class RepositoryQuery implements QueryInterface, SortRules, FilterColumns, Itera
     /**
      * Fetch and return the current row of this query's result
      *
-     * @return  object
+     * @return  mixed
      */
+    #[\ReturnTypeWillChange]
     public function current()
     {
         $row = $this->iterator->current();
@@ -763,7 +764,7 @@ class RepositoryQuery implements QueryInterface, SortRules, FilterColumns, Itera
      *
      * @return  bool
      */
-    public function valid()
+    public function valid(): bool
     {
         if (! $this->iterator->valid()) {
             Benchmark::measure('Query result iteration finished');
@@ -778,6 +779,7 @@ class RepositoryQuery implements QueryInterface, SortRules, FilterColumns, Itera
      *
      * @return  mixed
      */
+    #[\ReturnTypeWillChange]
     public function key()
     {
         return $this->iterator->key();
@@ -786,7 +788,7 @@ class RepositoryQuery implements QueryInterface, SortRules, FilterColumns, Itera
     /**
      * Advance to the next row of this query's result
      */
-    public function next()
+    public function next(): void
     {
         $this->iterator->next();
     }
diff --git a/library/Icinga/User/Preferences.php b/library/Icinga/User/Preferences.php
index 03a87f368..b09462bc5 100644
--- a/library/Icinga/User/Preferences.php
+++ b/library/Icinga/User/Preferences.php
@@ -49,7 +49,7 @@ class Preferences implements Countable
      *
      * @return  int     The number of preferences
      */
-    public function count()
+    public function count(): int
     {
         return count($this->preferences);
     }
diff --git a/library/Icinga/Util/DirectoryIterator.php b/library/Icinga/Util/DirectoryIterator.php
index 60368733e..a2bed1c27 100644
--- a/library/Icinga/Util/DirectoryIterator.php
+++ b/library/Icinga/Util/DirectoryIterator.php
@@ -50,7 +50,7 @@ class DirectoryIterator implements RecursiveIterator
     /**
      * Current key
      *
-     * @var string
+     * @var string|false
      */
     private $key;
 
@@ -122,35 +122,23 @@ class DirectoryIterator implements RecursiveIterator
         return is_dir($path) && is_readable($path);
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function hasChildren()
+    public function hasChildren(): bool
     {
         return static::isReadable($this->current);
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function getChildren()
+    public function getChildren(): DirectoryIterator
     {
         return new static($this->current, $this->extension, $this->flags);
     }
 
-
-    /**
-     * {@inheritdoc}
-     */
+    #[\ReturnTypeWillChange]
     public function current()
     {
         return $this->current;
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function next()
+    public function next(): void
     {
         do {
             $this->files->next();
@@ -200,26 +188,18 @@ class DirectoryIterator implements RecursiveIterator
         $this->key = $file;
     }
 
-    /**
-     * {@inheritdoc}
-     */
+    #[\ReturnTypeWillChange]
     public function key()
     {
         return $this->key;
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function valid()
+    public function valid(): bool
     {
         return $this->current !== false;
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function rewind()
+    public function rewind(): void
     {
         if ($this->files === null) {
             $files = scandir($this->path);
diff --git a/library/Icinga/Util/EnumeratingFilterIterator.php b/library/Icinga/Util/EnumeratingFilterIterator.php
index bfb2abb94..065996105 100644
--- a/library/Icinga/Util/EnumeratingFilterIterator.php
+++ b/library/Icinga/Util/EnumeratingFilterIterator.php
@@ -17,19 +17,13 @@ abstract class EnumeratingFilterIterator extends FilterIterator
      */
     private $index;
 
-    /**
-     * @return void
-     */
-    public function rewind()
+    public function rewind(): void
     {
         parent::rewind();
         $this->index = 0;
     }
 
-    /**
-     * @return int
-     */
-    public function key()
+    public function key(): int
     {
         return $this->index++;
     }
diff --git a/library/Icinga/Util/File.php b/library/Icinga/Util/File.php
index 1dde440e9..dad332aea 100644
--- a/library/Icinga/Util/File.php
+++ b/library/Icinga/Util/File.php
@@ -114,9 +114,7 @@ class File extends SplFileObject
         }
     }
 
-    /**
-     * @see SplFileObject::fwrite()
-     */
+    #[\ReturnTypeWillChange]
     public function fwrite($str, $length = null)
     {
         $this->assertOpenForWriting();
@@ -126,10 +124,7 @@ class File extends SplFileObject
         return $retVal;
     }
 
-    /**
-     * @see SplFileObject::ftruncate()
-     */
-    public function ftruncate($size)
+    public function ftruncate($size): bool
     {
         $this->assertOpenForWriting();
         $this->setupErrorHandler();
@@ -138,9 +133,7 @@ class File extends SplFileObject
         return $retVal;
     }
 
-    /**
-     * @see SplFileObject::ftell()
-     */
+    #[\ReturnTypeWillChange]
     public function ftell()
     {
         $this->setupErrorHandler();
@@ -149,10 +142,7 @@ class File extends SplFileObject
         return $retVal;
     }
 
-    /**
-     * @see SplFileObject::flock()
-     */
-    public function flock($operation, &$wouldblock = null)
+    public function flock($operation, &$wouldblock = null): bool
     {
         $this->setupErrorHandler();
         $retVal = parent::flock($operation, $wouldblock);
@@ -160,9 +150,7 @@ class File extends SplFileObject
         return $retVal;
     }
 
-    /**
-     * @see SplFileObject::fgetc()
-     */
+    #[\ReturnTypeWillChange]
     public function fgetc()
     {
         $this->setupErrorHandler();
@@ -171,10 +159,7 @@ class File extends SplFileObject
         return $retVal;
     }
 
-    /**
-     * @see SplFileObject::fflush()
-     */
-    public function fflush()
+    public function fflush(): bool
     {
         $this->setupErrorHandler();
         $retVal = parent::fflush();
diff --git a/library/Icinga/Web/CookieSet.php b/library/Icinga/Web/CookieSet.php
index cbc5a430b..019be292b 100644
--- a/library/Icinga/Web/CookieSet.php
+++ b/library/Icinga/Web/CookieSet.php
@@ -5,6 +5,7 @@ namespace Icinga\Web;
 
 use ArrayIterator;
 use IteratorAggregate;
+use Traversable;
 
 /**
  * Maintain a set of cookies
@@ -23,7 +24,7 @@ class CookieSet implements IteratorAggregate
      *
      * @return  ArrayIterator   An iterator for traversing the cookies in this set
      */
-    public function getIterator()
+    public function getIterator(): Traversable
     {
         return new ArrayIterator($this->cookies);
     }
diff --git a/library/Icinga/Web/Dom/DomNodeIterator.php b/library/Icinga/Web/Dom/DomNodeIterator.php
index b6408751e..1ea20b8e0 100644
--- a/library/Icinga/Web/Dom/DomNodeIterator.php
+++ b/library/Icinga/Web/Dom/DomNodeIterator.php
@@ -47,59 +47,37 @@ class DomNodeIterator implements RecursiveIterator
         $this->children = new IteratorIterator($node->childNodes);
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function current()
+    public function current(): ?DOMNode
     {
         return $this->children->current();
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function key()
+    public function key(): int
     {
         return $this->children->key();
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function next()
+    public function next(): void
     {
         $this->children->next();
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function rewind()
+    public function rewind(): void
     {
         $this->children->rewind();
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function valid()
+    public function valid(): bool
     {
         return $this->children->valid();
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function hasChildren()
+    public function hasChildren(): bool
     {
         return $this->current()->hasChildNodes();
     }
 
-    /**
-     * {@inheritdoc}
-     * @return DomNodeIterator
-     */
-    public function getChildren()
+    public function getChildren(): DomNodeIterator
     {
         return new static($this->current());
     }
diff --git a/library/Icinga/Web/Navigation/Navigation.php b/library/Icinga/Web/Navigation/Navigation.php
index 423c51894..8cf3f6845 100644
--- a/library/Icinga/Web/Navigation/Navigation.php
+++ b/library/Icinga/Web/Navigation/Navigation.php
@@ -67,50 +67,32 @@ class Navigation implements ArrayAccess, Countable, IteratorAggregate
      */
     protected $layout;
 
-    /**
-     * {@inheritdoc}
-     */
-    public function offsetExists($offset)
+    public function offsetExists($offset): bool
     {
         return isset($this->items[$offset]);
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function offsetGet($offset)
+    public function offsetGet($offset): ?NavigationItem
     {
-        return isset($this->items[$offset]) ? $this->items[$offset] : null;
+        return $this->items[$offset] ?? null;
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function offsetSet($offset, $value)
+    public function offsetSet($offset, $value): void
     {
         $this->items[$offset] = $value;
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function offsetUnset($offset)
+    public function offsetUnset($offset): void
     {
         unset($this->items[$offset]);
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function count()
+    public function count(): int
     {
         return count($this->items);
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function getIterator()
+    public function getIterator(): Traversable
     {
         $this->order();
         return new ArrayIterator($this->items);
diff --git a/library/Icinga/Web/Navigation/NavigationItem.php b/library/Icinga/Web/Navigation/NavigationItem.php
index 27f465c93..e262f5af0 100644
--- a/library/Icinga/Web/Navigation/NavigationItem.php
+++ b/library/Icinga/Web/Navigation/NavigationItem.php
@@ -13,6 +13,7 @@ use Icinga\Exception\IcingaException;
 use Icinga\Exception\ProgrammingError;
 use Icinga\Web\Navigation\Renderer\NavigationItemRenderer;
 use Icinga\Web\Url;
+use Traversable;
 
 /**
  * A navigation item
@@ -171,9 +172,9 @@ class NavigationItem implements IteratorAggregate
     }
 
     /**
-     * {@inheritdoc}
+     * @return Navigation
      */
-    public function getIterator()
+    public function getIterator(): Traversable
     {
         return $this->getChildren();
     }
diff --git a/library/Icinga/Web/Navigation/Renderer/NavigationRenderer.php b/library/Icinga/Web/Navigation/Renderer/NavigationRenderer.php
index e2fb40b4f..00c0f9af2 100644
--- a/library/Icinga/Web/Navigation/Renderer/NavigationRenderer.php
+++ b/library/Icinga/Web/Navigation/Renderer/NavigationRenderer.php
@@ -165,52 +165,32 @@ class NavigationRenderer implements RecursiveIterator, NavigationRendererInterfa
         return $this;
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function getChildren()
+    public function getChildren(): NavigationRenderer
     {
         return new static($this->current()->getChildren(), $this->skipOuterElement);
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function hasChildren()
+    public function hasChildren(): bool
     {
         return $this->current()->hasChildren();
     }
 
-    /**
-     * {@inheritdoc}
-     *
-     * @return  NavigationItem
-     */
-    public function current()
+    public function current(): NavigationItem
     {
         return $this->iterator->current();
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function key()
+    public function key(): int
     {
         return $this->iterator->key();
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function next()
+    public function next(): void
     {
         $this->iterator->next();
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function rewind()
+    public function rewind(): void
     {
         $this->iterator->rewind();
         if (! $this->skipOuterElement) {
@@ -218,10 +198,7 @@ class NavigationRenderer implements RecursiveIterator, NavigationRendererInterfa
         }
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function valid()
+    public function valid(): bool
     {
         $valid = $this->iterator->valid();
         if (! $this->skipOuterElement && !$valid) {
diff --git a/library/Icinga/Web/Navigation/Renderer/RecursiveNavigationRenderer.php b/library/Icinga/Web/Navigation/Renderer/RecursiveNavigationRenderer.php
index 562ed37d6..315c2aa4d 100644
--- a/library/Icinga/Web/Navigation/Renderer/RecursiveNavigationRenderer.php
+++ b/library/Icinga/Web/Navigation/Renderer/RecursiveNavigationRenderer.php
@@ -121,34 +121,22 @@ class RecursiveNavigationRenderer extends RecursiveIteratorIterator implements N
         return $this->getInnerIterator()->getHeading();
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function beginIteration()
+    public function beginIteration(): void
     {
         $this->content[] = $this->getInnerIterator()->beginMarkup();
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function endIteration()
+    public function endIteration(): void
     {
         $this->content[] = $this->getInnerIterator()->endMarkup();
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function beginChildren()
+    public function beginChildren(): void
     {
         $this->content[] = $this->getInnerIterator()->beginChildrenMarkup($this->getDepth() + 1);
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function endChildren()
+    public function endChildren(): void
     {
         $this->content[] = $this->getInnerIterator()->endChildrenMarkup();
         $this->content[] = $this->getInnerIterator()->endItemMarkup();
diff --git a/library/Icinga/Web/Paginator/Adapter/QueryAdapter.php b/library/Icinga/Web/Paginator/Adapter/QueryAdapter.php
index 36d11ec83..6f103e5ab 100644
--- a/library/Icinga/Web/Paginator/Adapter/QueryAdapter.php
+++ b/library/Icinga/Web/Paginator/Adapter/QueryAdapter.php
@@ -73,7 +73,7 @@ class QueryAdapter implements Zend_Paginator_Adapter_Interface
      *
      * @return  int
      */
-    public function count()
+    public function count(): int
     {
         if ($this->count === null) {
             $this->count = $this->query->count();
diff --git a/library/Icinga/Web/Session/SessionNamespace.php b/library/Icinga/Web/Session/SessionNamespace.php
index 19083c05f..1c9c13f7a 100644
--- a/library/Icinga/Web/Session/SessionNamespace.php
+++ b/library/Icinga/Web/Session/SessionNamespace.php
@@ -7,6 +7,7 @@ use Exception;
 use ArrayIterator;
 use Icinga\Exception\IcingaException;
 use IteratorAggregate;
+use Traversable;
 
 /**
  * Container for session values
@@ -32,7 +33,7 @@ class SessionNamespace implements IteratorAggregate
      *
      * @return  ArrayIterator
      */
-    public function getIterator()
+    public function getIterator(): Traversable
     {
         return new ArrayIterator($this->getAll());
     }
diff --git a/library/Icinga/Web/Widget/Tabs.php b/library/Icinga/Web/Widget/Tabs.php
index f490302a8..5daf86afb 100644
--- a/library/Icinga/Web/Widget/Tabs.php
+++ b/library/Icinga/Web/Widget/Tabs.php
@@ -403,7 +403,7 @@ EOT;
      *
      * @see     Countable
      */
-    public function count()
+    public function count(): int
     {
         return count($this->tabs);
     }
diff --git a/library/vendor/Zend/Controller/Action/HelperBroker/PriorityStack.php b/library/vendor/Zend/Controller/Action/HelperBroker/PriorityStack.php
index 8f5193f21..c957b10d5 100644
--- a/library/vendor/Zend/Controller/Action/HelperBroker/PriorityStack.php
+++ b/library/vendor/Zend/Controller/Action/HelperBroker/PriorityStack.php
@@ -64,11 +64,10 @@ class Zend_Controller_Action_HelperBroker_PriorityStack implements IteratorAggre
      * Magic property overloading for unsetting if helper is exists by name
      *
      * @param string $helperName    The helper name
-     * @return Zend_Controller_Action_Helper_Abstract
      */
     public function __unset($helperName)
     {
-        return $this->offsetUnset($helperName);
+        $this->offsetUnset($helperName);
     }
 
     /**
@@ -86,9 +85,9 @@ class Zend_Controller_Action_HelperBroker_PriorityStack implements IteratorAggre
     /**
      * Return something iterable
      *
-     * @return array
+     * @return Traversable
      */
-    public function getIterator()
+    public function getIterator(): Traversable
     {
         return new ArrayObject($this->_helpersByPriority);
     }
@@ -97,9 +96,9 @@ class Zend_Controller_Action_HelperBroker_PriorityStack implements IteratorAggre
      * offsetExists()
      *
      * @param int|string $priorityOrHelperName
-     * @return Zend_Controller_Action_HelperBroker_PriorityStack
+     * @return bool
      */
-    public function offsetExists($priorityOrHelperName)
+    public function offsetExists($priorityOrHelperName): bool
     {
         if (is_string($priorityOrHelperName)) {
             return array_key_exists($priorityOrHelperName, $this->_helpersByNameRef);
@@ -112,9 +111,9 @@ class Zend_Controller_Action_HelperBroker_PriorityStack implements IteratorAggre
      * offsetGet()
      *
      * @param int|string $priorityOrHelperName
-     * @return Zend_Controller_Action_HelperBroker_PriorityStack
+     * @return Zend_Controller_Action_Helper_Abstract
      */
-    public function offsetGet($priorityOrHelperName)
+    public function offsetGet($priorityOrHelperName): Zend_Controller_Action_Helper_Abstract
     {
         if (!$this->offsetExists($priorityOrHelperName)) {
             throw new Zend_Controller_Action_Exception('A helper with priority ' . $priorityOrHelperName . ' does not exist.');
@@ -132,9 +131,8 @@ class Zend_Controller_Action_HelperBroker_PriorityStack implements IteratorAggre
      *
      * @param int $priority
      * @param Zend_Controller_Action_Helper_Abstract $helper
-     * @return Zend_Controller_Action_HelperBroker_PriorityStack
      */
-    public function offsetSet($priority, $helper)
+    public function offsetSet($priority, $helper): void
     {
         $priority = (int) $priority;
 
@@ -161,16 +159,14 @@ class Zend_Controller_Action_HelperBroker_PriorityStack implements IteratorAggre
         }
 
         krsort($this->_helpersByPriority);  // always make sure priority and LIFO are both enforced
-        return $this;
     }
 
     /**
      * offsetUnset()
      *
      * @param int|string $priorityOrHelperName Priority integer or the helper name
-     * @return Zend_Controller_Action_HelperBroker_PriorityStack
      */
-    public function offsetUnset($priorityOrHelperName)
+    public function offsetUnset($priorityOrHelperName): void
     {
         if (!$this->offsetExists($priorityOrHelperName)) {
             throw new Zend_Controller_Action_Exception('A helper with priority or name ' . $priorityOrHelperName . ' does not exist.');
@@ -187,7 +183,6 @@ class Zend_Controller_Action_HelperBroker_PriorityStack implements IteratorAggre
 
         unset($this->_helpersByNameRef[$helperName]);
         unset($this->_helpersByPriority[$priority]);
-        return $this;
     }
 
     /**
@@ -195,7 +190,7 @@ class Zend_Controller_Action_HelperBroker_PriorityStack implements IteratorAggre
      *
      * @return int
      */
-    public function count()
+    public function count(): int
     {
         return count($this->_helpersByPriority);
     }
diff --git a/library/vendor/Zend/Db/Statement/Pdo.php b/library/vendor/Zend/Db/Statement/Pdo.php
index 5b63a17f0..cf0150a59 100644
--- a/library/vendor/Zend/Db/Statement/Pdo.php
+++ b/library/vendor/Zend/Db/Statement/Pdo.php
@@ -252,7 +252,7 @@ class Zend_Db_Statement_Pdo extends Zend_Db_Statement implements IteratorAggrega
      *
      * @return IteratorIterator
      */
-    public function getIterator()
+    public function getIterator(): Traversable
     {
         return new IteratorIterator($this->_stmt);
     }
diff --git a/library/vendor/Zend/Form.php b/library/vendor/Zend/Form.php
index bd373b41b..213ad301f 100644
--- a/library/vendor/Zend/Form.php
+++ b/library/vendor/Zend/Form.php
@@ -3246,6 +3246,7 @@ class Zend_Form implements Iterator, Countable, Zend_Validate_Interface
      * @throws Zend_Form_Exception
      * @return Zend_Form_Element|Zend_Form_DisplayGroup|Zend_Form
      */
+    #[\ReturnTypeWillChange]
     public function current()
     {
         $this->_sort();
@@ -3268,7 +3269,7 @@ class Zend_Form implements Iterator, Countable, Zend_Validate_Interface
      *
      * @return string
      */
-    public function key()
+    public function key(): string
     {
         $this->_sort();
         return key($this->_order);
@@ -3279,7 +3280,7 @@ class Zend_Form implements Iterator, Countable, Zend_Validate_Interface
      *
      * @return void
      */
-    public function next()
+    public function next(): void
     {
         $this->_sort();
         next($this->_order);
@@ -3290,7 +3291,7 @@ class Zend_Form implements Iterator, Countable, Zend_Validate_Interface
      *
      * @return void
      */
-    public function rewind()
+    public function rewind(): void
     {
         $this->_sort();
         reset($this->_order);
@@ -3301,7 +3302,7 @@ class Zend_Form implements Iterator, Countable, Zend_Validate_Interface
      *
      * @return bool
      */
-    public function valid()
+    public function valid(): bool
     {
         $this->_sort();
         return (current($this->_order) !== false);
@@ -3312,7 +3313,7 @@ class Zend_Form implements Iterator, Countable, Zend_Validate_Interface
      *
      * @return int
      */
-    public function count()
+    public function count(): int
     {
         return count($this->_order);
     }
diff --git a/library/vendor/Zend/Form/DisplayGroup.php b/library/vendor/Zend/Form/DisplayGroup.php
index 4adc4f32d..73a4cdee6 100644
--- a/library/vendor/Zend/Form/DisplayGroup.php
+++ b/library/vendor/Zend/Form/DisplayGroup.php
@@ -1036,7 +1036,7 @@ class Zend_Form_DisplayGroup implements Iterator,Countable
      *
      * @return Zend_Form_Element
      */
-    public function current()
+    public function current(): Zend_Form_Element
     {
         $this->_sort();
         current($this->_elementOrder);
@@ -1049,7 +1049,7 @@ class Zend_Form_DisplayGroup implements Iterator,Countable
      *
      * @return string
      */
-    public function key()
+    public function key(): string
     {
         $this->_sort();
         return key($this->_elementOrder);
@@ -1060,7 +1060,7 @@ class Zend_Form_DisplayGroup implements Iterator,Countable
      *
      * @return void
      */
-    public function next()
+    public function next(): void
     {
         $this->_sort();
         next($this->_elementOrder);
@@ -1071,7 +1071,7 @@ class Zend_Form_DisplayGroup implements Iterator,Countable
      *
      * @return void
      */
-    public function rewind()
+    public function rewind(): void
     {
         $this->_sort();
         reset($this->_elementOrder);
@@ -1082,7 +1082,7 @@ class Zend_Form_DisplayGroup implements Iterator,Countable
      *
      * @return bool
      */
-    public function valid()
+    public function valid(): bool
     {
         $this->_sort();
         return (current($this->_elementOrder) !== false);
@@ -1093,7 +1093,7 @@ class Zend_Form_DisplayGroup implements Iterator,Countable
      *
      * @return int
      */
-    public function count()
+    public function count(): int
     {
         return count($this->_elements);
     }
diff --git a/library/vendor/Zend/Paginator.php b/library/vendor/Zend/Paginator.php
index 49ffb9d1e..e96f88203 100644
--- a/library/vendor/Zend/Paginator.php
+++ b/library/vendor/Zend/Paginator.php
@@ -510,7 +510,7 @@ class Zend_Paginator implements Countable, IteratorAggregate
      *
      * @return integer
      */
-    public function count()
+    public function count(): int
     {
         if (!$this->_pageCount) {
             $this->_pageCount = $this->_calculatePageCount();
@@ -812,7 +812,7 @@ class Zend_Paginator implements Countable, IteratorAggregate
      *
      * @return Traversable
      */
-    public function getIterator()
+    public function getIterator(): Traversable
     {
         return $this->getCurrentItems();
     }
diff --git a/library/vendor/Zend/Paginator/SerializableLimitIterator.php b/library/vendor/Zend/Paginator/SerializableLimitIterator.php
index 72c1399c9..504a342e3 100644
--- a/library/vendor/Zend/Paginator/SerializableLimitIterator.php
+++ b/library/vendor/Zend/Paginator/SerializableLimitIterator.php
@@ -86,6 +86,7 @@ class Zend_Paginator_SerializableLimitIterator extends LimitIterator implements
      * @param int $offset
      * @return mixed
      */
+    #[\ReturnTypeWillChange]
     public function offsetGet($offset)
     {
         $currentOffset = $this->key();
@@ -102,7 +103,7 @@ class Zend_Paginator_SerializableLimitIterator extends LimitIterator implements
      * @param int $offset
      * @param mixed $value
      */
-    public function offsetSet($offset, $value)
+    public function offsetSet($offset, $value): void
     {
     }
 
@@ -111,7 +112,7 @@ class Zend_Paginator_SerializableLimitIterator extends LimitIterator implements
      *
      * @param int $offset
      */
-    public function offsetExists($offset)
+    public function offsetExists($offset): bool
     {
         if ($offset > 0 && $offset < $this->_count) {
             try {
@@ -136,7 +137,7 @@ class Zend_Paginator_SerializableLimitIterator extends LimitIterator implements
      *
      * @param int $offset
      */
-    public function offsetUnset($offset)
+    public function offsetUnset($offset): void
     {
     }
 }
diff --git a/library/vendor/Zend/View/Helper/HeadLink.php b/library/vendor/Zend/View/Helper/HeadLink.php
index 1a15d177d..3b1bcb7f1 100644
--- a/library/vendor/Zend/View/Helper/HeadLink.php
+++ b/library/vendor/Zend/View/Helper/HeadLink.php
@@ -230,7 +230,7 @@ class Zend_View_Helper_HeadLink extends Zend_View_Helper_Placeholder_Container_S
      * @param  array $value
      * @return void
      */
-    public function offsetSet($index, $value)
+    public function offsetSet($index, $value): void
     {
         if (!$this->_isValid($value)) {
             $e = new Zend_View_Exception('offsetSet() expects a data token; please use one of the custom offsetSet*() methods');
@@ -238,7 +238,7 @@ class Zend_View_Helper_HeadLink extends Zend_View_Helper_Placeholder_Container_S
             throw $e;
         }
 
-        return $this->getContainer()->offsetSet($index, $value);
+        $this->getContainer()->offsetSet($index, $value);
     }
 
     /**
diff --git a/library/vendor/Zend/View/Helper/HeadMeta.php b/library/vendor/Zend/View/Helper/HeadMeta.php
index bb112559f..88cd3a7a2 100644
--- a/library/vendor/Zend/View/Helper/HeadMeta.php
+++ b/library/vendor/Zend/View/Helper/HeadMeta.php
@@ -168,7 +168,8 @@ class Zend_View_Helper_HeadMeta extends Zend_View_Helper_Placeholder_Container_S
             $item  = $this->createData($type, $args[0], $args[1], $args[2]);
 
             if ('offsetSet' == $action) {
-                return $this->offsetSet($index, $item);
+                $this->offsetSet($index, $item);
+                return $this;
             }
 
             $this->$action($item);
@@ -254,7 +255,7 @@ class Zend_View_Helper_HeadMeta extends Zend_View_Helper_Placeholder_Container_S
      * @return void
      * @throws Zend_View_Exception
      */
-    public function offsetSet($index, $value)
+    public function offsetSet($index, $value): void
     {
         if (!$this->_isValid($value)) {
             $e =  new Zend_View_Exception('Invalid value passed to offsetSet; please use offsetSetName() or offsetSetHttpEquiv()');
@@ -262,7 +263,7 @@ class Zend_View_Helper_HeadMeta extends Zend_View_Helper_Placeholder_Container_S
             throw $e;
         }
 
-        return $this->getContainer()->offsetSet($index, $value);
+        $this->getContainer()->offsetSet($index, $value);
     }
 
     /**
@@ -272,7 +273,7 @@ class Zend_View_Helper_HeadMeta extends Zend_View_Helper_Placeholder_Container_S
      * @return void
      * @throws Zend_View_Exception
      */
-    public function offsetUnset($index)
+    public function offsetUnset($index): void
     {
         if (!in_array($index, $this->getContainer()->getKeys())) {
             $e = new Zend_View_Exception('Invalid index passed to offsetUnset()');
@@ -280,7 +281,7 @@ class Zend_View_Helper_HeadMeta extends Zend_View_Helper_Placeholder_Container_S
             throw $e;
         }
 
-        return $this->getContainer()->offsetUnset($index);
+        $this->getContainer()->offsetUnset($index);
     }
 
     /**
diff --git a/library/vendor/Zend/View/Helper/HeadScript.php b/library/vendor/Zend/View/Helper/HeadScript.php
index 95a036577..5b8461d0b 100644
--- a/library/vendor/Zend/View/Helper/HeadScript.php
+++ b/library/vendor/Zend/View/Helper/HeadScript.php
@@ -363,7 +363,7 @@ class Zend_View_Helper_HeadScript extends Zend_View_Helper_Placeholder_Container
      * @param  mixed $value
      * @return void
      */
-    public function offsetSet($index, $value)
+    public function offsetSet($index, $value): void
     {
         if (!$this->_isValid($value)) {
             $e = new Zend_View_Exception('Invalid argument passed to offsetSet(); please use one of the helper methods, offsetSetScript() or offsetSetFile()');
@@ -371,7 +371,7 @@ class Zend_View_Helper_HeadScript extends Zend_View_Helper_Placeholder_Container
             throw $e;
         }
 
-        return $this->getContainer()->offsetSet($index, $value);
+        $this->getContainer()->offsetSet($index, $value);
     }
 
     /**
diff --git a/library/vendor/Zend/View/Helper/HeadStyle.php b/library/vendor/Zend/View/Helper/HeadStyle.php
index 933490166..c28f99701 100644
--- a/library/vendor/Zend/View/Helper/HeadStyle.php
+++ b/library/vendor/Zend/View/Helper/HeadStyle.php
@@ -217,7 +217,7 @@ class Zend_View_Helper_HeadStyle extends Zend_View_Helper_Placeholder_Container_
      * @param  mixed $value
      * @return void
      */
-    public function offsetSet($index, $value)
+    public function offsetSet($index, $value): void
     {
         if (!$this->_isValid($value)) {
             $e = new Zend_View_Exception('Invalid value passed to offsetSet; please use offsetSetStyle()');
@@ -225,7 +225,7 @@ class Zend_View_Helper_HeadStyle extends Zend_View_Helper_Placeholder_Container_
             throw $e;
         }
 
-        return $this->getContainer()->offsetSet($index, $value);
+        $this->getContainer()->offsetSet($index, $value);
     }
 
     /**
diff --git a/library/vendor/Zend/View/Helper/Placeholder/Container/Standalone.php b/library/vendor/Zend/View/Helper/Placeholder/Container/Standalone.php
index c452f0319..c875ca78a 100644
--- a/library/vendor/Zend/View/Helper/Placeholder/Container/Standalone.php
+++ b/library/vendor/Zend/View/Helper/Placeholder/Container/Standalone.php
@@ -258,7 +258,7 @@ abstract class Zend_View_Helper_Placeholder_Container_Standalone extends Zend_Vi
      *
      * @return int
      */
-    public function count()
+    public function count(): int
     {
         $container = $this->getContainer();
         return count($container);
@@ -270,7 +270,7 @@ abstract class Zend_View_Helper_Placeholder_Container_Standalone extends Zend_Vi
      * @param  string|int $offset
      * @return bool
      */
-    public function offsetExists($offset)
+    public function offsetExists($offset): bool
     {
         return $this->getContainer()->offsetExists($offset);
     }
@@ -281,6 +281,7 @@ abstract class Zend_View_Helper_Placeholder_Container_Standalone extends Zend_Vi
      * @param  string|int $offset
      * @return mixed
      */
+    #[\ReturnTypeWillChange]
     public function offsetGet($offset)
     {
         return $this->getContainer()->offsetGet($offset);
@@ -293,9 +294,9 @@ abstract class Zend_View_Helper_Placeholder_Container_Standalone extends Zend_Vi
      * @param  mixed $value
      * @return void
      */
-    public function offsetSet($offset, $value)
+    public function offsetSet($offset, $value): void
     {
-        return $this->getContainer()->offsetSet($offset, $value);
+        $this->getContainer()->offsetSet($offset, $value);
     }
 
     /**
@@ -304,9 +305,9 @@ abstract class Zend_View_Helper_Placeholder_Container_Standalone extends Zend_Vi
      * @param  string|int $offset
      * @return void
      */
-    public function offsetUnset($offset)
+    public function offsetUnset($offset): void
     {
-        return $this->getContainer()->offsetUnset($offset);
+        $this->getContainer()->offsetUnset($offset);
     }
 
     /**
@@ -314,7 +315,7 @@ abstract class Zend_View_Helper_Placeholder_Container_Standalone extends Zend_Vi
      *
      * @return Iterator
      */
-    public function getIterator()
+    public function getIterator(): Traversable
     {
         return $this->getContainer()->getIterator();
     }
diff --git a/modules/doc/library/Doc/DocSectionFilterIterator.php b/modules/doc/library/Doc/DocSectionFilterIterator.php
index 3ca1c4854..bac5a6742 100644
--- a/modules/doc/library/Doc/DocSectionFilterIterator.php
+++ b/modules/doc/library/Doc/DocSectionFilterIterator.php
@@ -41,7 +41,7 @@ class DocSectionFilterIterator extends RecursiveFilterIterator implements Counta
      * @return bool Whether the current element of the iterator is acceptable
      *              through this filter
      */
-    public function accept()
+    public function accept(): bool
     {
         $section = $this->current();
         /** @var \Icinga\Module\Doc\DocSection $section */
@@ -51,18 +51,12 @@ class DocSectionFilterIterator extends RecursiveFilterIterator implements Counta
         return false;
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function getChildren()
+    public function getChildren(): self
     {
         return new static($this->getInnerIterator()->getChildren(), $this->chapter);
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function count()
+    public function count(): int
     {
         return iterator_count($this);
     }
diff --git a/modules/doc/library/Doc/Renderer/DocSearchRenderer.php b/modules/doc/library/Doc/Renderer/DocSearchRenderer.php
index 79d2dfd86..c6e9ae2fd 100644
--- a/modules/doc/library/Doc/Renderer/DocSearchRenderer.php
+++ b/modules/doc/library/Doc/Renderer/DocSearchRenderer.php
@@ -9,10 +9,6 @@ use Icinga\Module\Doc\Search\DocSearchMatch;
 
 /**
  * Renderer for doc searches
- *
- * @method DocSearchIterator getInnerIterator() {
- *     @{inheritdoc}
- * }
  */
 class DocSearchRenderer extends DocRenderer
 {
@@ -33,45 +29,30 @@ class DocSearchRenderer extends DocRenderer
         parent::__construct($iterator, RecursiveIteratorIterator::SELF_FIRST);
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function beginIteration()
+    public function beginIteration(): void
     {
         $this->content[] = '<nav role="navigation"><ul class="toc">';
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function endIteration()
+    public function endIteration(): void
     {
         $this->content[] = '</ul></nav>';
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function beginChildren()
+    public function beginChildren(): void
     {
         if ($this->getInnerIterator()->getMatches()) {
             $this->content[] = '<ul class="toc">';
         }
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function endChildren()
+    public function endChildren(): void
     {
         if ($this->getInnerIterator()->getMatches()) {
             $this->content[] = '</ul>';
         }
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function render()
     {
         foreach ($this as $section) {
diff --git a/modules/doc/library/Doc/Renderer/DocTocRenderer.php b/modules/doc/library/Doc/Renderer/DocTocRenderer.php
index 613461c86..09e9a1d81 100644
--- a/modules/doc/library/Doc/Renderer/DocTocRenderer.php
+++ b/modules/doc/library/Doc/Renderer/DocTocRenderer.php
@@ -3,16 +3,11 @@
 
 namespace Icinga\Module\Doc\Renderer;
 
-use Icinga\Web\View;
 use Icinga\Data\Tree\TreeNodeIterator;
 use RecursiveIteratorIterator;
 
 /**
  * TOC renderer
- *
- * @method TreeNodeIterator getInnerIterator() {
- *     {@inheritdoc}
- * }
  */
 class DocTocRenderer extends DocRenderer
 {
@@ -47,41 +42,26 @@ class DocTocRenderer extends DocRenderer
         parent::__construct($iterator, RecursiveIteratorIterator::SELF_FIRST);
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function beginIteration()
+    public function beginIteration(): void
     {
         $this->content[] = sprintf('<nav role="navigation"><%s class="%s">', static::HTML_LIST_TAG, static::CSS_CLASS);
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function endIteration()
+    public function endIteration(): void
     {
         $this->content[] = sprintf('</%s></nav>', static::HTML_LIST_TAG);
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function beginChildren()
+    public function beginChildren(): void
     {
         $this->content[] = sprintf('<%s class="%s">', static::HTML_LIST_TAG, static::CSS_CLASS);
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function endChildren()
+    public function endChildren(): void
     {
         $this->content[] = sprintf('</%s>', static::HTML_LIST_TAG);
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function render()
     {
         if ($this->getInnerIterator()->isEmpty()) {
diff --git a/modules/doc/library/Doc/Search/DocSearchIterator.php b/modules/doc/library/Doc/Search/DocSearchIterator.php
index 45a93ea0e..e46de3624 100644
--- a/modules/doc/library/Doc/Search/DocSearchIterator.php
+++ b/modules/doc/library/Doc/Search/DocSearchIterator.php
@@ -9,10 +9,6 @@ use Icinga\Data\Tree\TreeNodeIterator;
 
 /**
  * Iterator over doc sections that match a given search criteria
- *
- * @method TreeNodeIterator getInnerIterator() {
- *     {@inheritdoc}
- * }
  */
 class DocSearchIterator extends RecursiveFilterIterator
 {
@@ -48,7 +44,7 @@ class DocSearchIterator extends RecursiveFilterIterator
      * @return bool Whether the current element of the iterator is acceptable
      *              through this filter
      */
-    public function accept()
+    public function accept(): bool
     {
         $section = $this->current();
         /** @var $section \Icinga\Module\Doc\DocSection */
@@ -84,10 +80,7 @@ class DocSearchIterator extends RecursiveFilterIterator
         return $this->search;
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function getChildren()
+    public function getChildren(): self
     {
         return new static($this->getInnerIterator()->getChildren(), $this->search);
     }
diff --git a/modules/monitoring/library/Monitoring/Data/ColumnFilterIterator.php b/modules/monitoring/library/Monitoring/Data/ColumnFilterIterator.php
index 95555cd6c..0ad051b9b 100644
--- a/modules/monitoring/library/Monitoring/Data/ColumnFilterIterator.php
+++ b/modules/monitoring/library/Monitoring/Data/ColumnFilterIterator.php
@@ -22,10 +22,7 @@ class ColumnFilterIterator extends FilterIterator
         parent::__construct(new ArrayIterator($columns));
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function accept()
+    public function accept(): bool
     {
         $column = $this->current();
         return ! ($column instanceof Zend_Db_Expr || $column === '(NULL)');
diff --git a/modules/monitoring/library/Monitoring/Data/CustomvarProtectionIterator.php b/modules/monitoring/library/Monitoring/Data/CustomvarProtectionIterator.php
index 5d62afff9..c3cc01a69 100644
--- a/modules/monitoring/library/Monitoring/Data/CustomvarProtectionIterator.php
+++ b/modules/monitoring/library/Monitoring/Data/CustomvarProtectionIterator.php
@@ -10,7 +10,7 @@ class CustomvarProtectionIterator extends IteratorIterator
 {
     const IS_CV_RE = '~^_(host|service)_([a-zA-Z0-9_]+)$~';
 
-    public function current()
+    public function current(): object
     {
         $row = parent::current();
 
diff --git a/modules/monitoring/library/Monitoring/DataView/DataView.php b/modules/monitoring/library/Monitoring/DataView/DataView.php
index 39c5305b1..e16656ec6 100644
--- a/modules/monitoring/library/Monitoring/DataView/DataView.php
+++ b/modules/monitoring/library/Monitoring/DataView/DataView.php
@@ -17,6 +17,7 @@ use Icinga\Module\Monitoring\Backend\Ido\Query\IdoQuery;
 use Icinga\Module\Monitoring\Backend\MonitoringBackend;
 use Icinga\Web\Request;
 use Icinga\Web\Url;
+use Traversable;
 
 /**
  * A read-only view of an underlying query
@@ -58,7 +59,7 @@ abstract class DataView implements QueryInterface, SortRules, FilterColumns, Ite
      *
      * @return  IdoQuery
      */
-    public function getIterator()
+    public function getIterator(): Traversable
     {
         return $this->getQuery();
     }
@@ -499,7 +500,7 @@ abstract class DataView implements QueryInterface, SortRules, FilterColumns, Ite
      *
      * @return int
      */
-    public function count()
+    public function count(): int
     {
         return $this->query->count();
     }
diff --git a/modules/monitoring/library/Monitoring/Object/ObjectList.php b/modules/monitoring/library/Monitoring/Object/ObjectList.php
index b2fd2dea2..36b922ae6 100644
--- a/modules/monitoring/library/Monitoring/Object/ObjectList.php
+++ b/modules/monitoring/library/Monitoring/Object/ObjectList.php
@@ -9,6 +9,7 @@ use Icinga\Data\Filter\Filter;
 use Icinga\Data\Filterable;
 use IteratorAggregate;
 use Icinga\Module\Monitoring\Backend\MonitoringBackend;
+use Traversable;
 
 abstract class ObjectList implements Countable, IteratorAggregate, Filterable
 {
@@ -118,10 +119,7 @@ abstract class ObjectList implements Countable, IteratorAggregate, Filterable
         return $this->objects;
     }
 
-    /**
-     * @return int
-     */
-    public function count()
+    public function count(): int
     {
         if ($this->count === null) {
             $this->count = (int) $this->backend
@@ -135,7 +133,7 @@ abstract class ObjectList implements Countable, IteratorAggregate, Filterable
         return $this->count;
     }
 
-    public function getIterator()
+    public function getIterator(): Traversable
     {
         if ($this->objects === null) {
             $this->fetch();
diff --git a/modules/monitoring/library/Monitoring/Plugin/PerfdataSet.php b/modules/monitoring/library/Monitoring/Plugin/PerfdataSet.php
index 5a865cc65..cc545a234 100644
--- a/modules/monitoring/library/Monitoring/Plugin/PerfdataSet.php
+++ b/modules/monitoring/library/Monitoring/Plugin/PerfdataSet.php
@@ -5,6 +5,7 @@ namespace Icinga\Module\Monitoring\Plugin;
 
 use ArrayIterator;
 use IteratorAggregate;
+use Traversable;
 
 class PerfdataSet implements IteratorAggregate
 {
@@ -47,7 +48,7 @@ class PerfdataSet implements IteratorAggregate
      *
      * @return  ArrayIterator
      */
-    public function getIterator()
+    public function getIterator(): Traversable
     {
         return new ArrayIterator($this->asArray());
     }
diff --git a/modules/monitoring/library/Monitoring/Timeline/TimeLine.php b/modules/monitoring/library/Monitoring/Timeline/TimeLine.php
index d1a98fc40..128b64bba 100644
--- a/modules/monitoring/library/Monitoring/Timeline/TimeLine.php
+++ b/modules/monitoring/library/Monitoring/Timeline/TimeLine.php
@@ -12,6 +12,7 @@ use Icinga\Data\Filter\Filter;
 use Icinga\Web\Hook;
 use Icinga\Web\Session\SessionNamespace;
 use Icinga\Module\Monitoring\DataView\DataView;
+use Traversable;
 
 /**
  * Represents a set of events in a specific range of time
@@ -100,7 +101,7 @@ class TimeLine implements IteratorAggregate
      *
      * @return  ArrayIterator
      */
-    public function getIterator()
+    public function getIterator(): Traversable
     {
         return new ArrayIterator($this->toArray());
     }
diff --git a/modules/monitoring/library/Monitoring/Timeline/TimeRange.php b/modules/monitoring/library/Monitoring/Timeline/TimeRange.php
index 945d99c8d..26d72505e 100644
--- a/modules/monitoring/library/Monitoring/Timeline/TimeRange.php
+++ b/modules/monitoring/library/Monitoring/Timeline/TimeRange.php
@@ -207,7 +207,7 @@ class TimeRange implements Iterator
     /**
      * Reset the iterator to its initial state
      */
-    public function rewind()
+    public function rewind(): void
     {
         $this->current = clone $this->start;
     }
@@ -217,7 +217,7 @@ class TimeRange implements Iterator
      *
      * @return  bool
      */
-    public function valid()
+    public function valid(): bool
     {
         if ($this->negative) {
             return $this->current > $this->end;
@@ -231,7 +231,7 @@ class TimeRange implements Iterator
      *
      * @return  StdClass
      */
-    public function current()
+    public function current(): object
     {
         return $this->getTimeframe($this->current);
     }
@@ -241,7 +241,7 @@ class TimeRange implements Iterator
      *
      * @return  int
      */
-    public function key()
+    public function key(): int
     {
         return $this->current->getTimestamp();
     }
@@ -249,7 +249,7 @@ class TimeRange implements Iterator
     /**
      * Advance the iterator position by one
      */
-    public function next()
+    public function next(): void
     {
         $this->applyInterval($this->current, 0);
     }
diff --git a/modules/setup/library/Setup/RequirementSet.php b/modules/setup/library/Setup/RequirementSet.php
index faf4d3199..4c5bb121a 100644
--- a/modules/setup/library/Setup/RequirementSet.php
+++ b/modules/setup/library/Setup/RequirementSet.php
@@ -5,6 +5,7 @@ namespace Icinga\Module\Setup;
 
 use LogicException;
 use RecursiveIterator;
+use Traversable;
 
 /**
  * Container to store and handle requirements
@@ -258,7 +259,7 @@ class RequirementSet implements RecursiveIterator
      *
      * @return  bool
      */
-    public function hasChildren()
+    public function hasChildren(): bool
     {
         $current = $this->current();
         return $current instanceof static;
@@ -267,9 +268,9 @@ class RequirementSet implements RecursiveIterator
     /**
      * Return a iterator for the current nested set of requirements
      *
-     * @return  RecursiveIterator
+     * @return  ?RecursiveIterator
      */
-    public function getChildren()
+    public function getChildren(): ?RecursiveIterator
     {
         return $this->current();
     }
@@ -277,7 +278,7 @@ class RequirementSet implements RecursiveIterator
     /**
      * Rewind the iterator to its first element
      */
-    public function rewind()
+    public function rewind(): void
     {
         reset($this->requirements);
     }
@@ -287,7 +288,7 @@ class RequirementSet implements RecursiveIterator
      *
      * @return  bool
      */
-    public function valid()
+    public function valid(): bool
     {
         return $this->key() !== null;
     }
@@ -297,6 +298,7 @@ class RequirementSet implements RecursiveIterator
      *
      * @return  Requirement|RequirementSet
      */
+    #[\ReturnTypeWillChange]
     public function current()
     {
         return current($this->requirements);
@@ -307,7 +309,7 @@ class RequirementSet implements RecursiveIterator
      *
      * @return  int
      */
-    public function key()
+    public function key(): int
     {
         return key($this->requirements);
     }
@@ -315,7 +317,7 @@ class RequirementSet implements RecursiveIterator
     /**
      * Advance the iterator to the next element
      */
-    public function next()
+    public function next(): void
     {
         next($this->requirements);
     }
diff --git a/modules/setup/library/Setup/RequirementsRenderer.php b/modules/setup/library/Setup/RequirementsRenderer.php
index ac4300206..cc9392a1a 100644
--- a/modules/setup/library/Setup/RequirementsRenderer.php
+++ b/modules/setup/library/Setup/RequirementsRenderer.php
@@ -7,17 +7,17 @@ use RecursiveIteratorIterator;
 
 class RequirementsRenderer extends RecursiveIteratorIterator
 {
-    public function beginIteration()
+    public function beginIteration(): void
     {
         $this->tags[] = '<ul class="requirements">';
     }
 
-    public function endIteration()
+    public function endIteration(): void
     {
         $this->tags[] = '</ul>';
     }
 
-    public function beginChildren()
+    public function beginChildren(): void
     {
         $this->tags[] = '<li>';
         $currentSet = $this->getSubIterator();
@@ -25,7 +25,7 @@ class RequirementsRenderer extends RecursiveIteratorIterator
         $this->tags[] = '<ul class="set-state ' . $state . '">';
     }
 
-    public function endChildren()
+    public function endChildren(): void
     {
         $this->tags[] = '</ul>';
         $this->tags[] = '</li>';
diff --git a/modules/setup/library/Setup/Setup.php b/modules/setup/library/Setup/Setup.php
index 9e88d590c..7b0baed36 100644
--- a/modules/setup/library/Setup/Setup.php
+++ b/modules/setup/library/Setup/Setup.php
@@ -6,6 +6,7 @@ namespace Icinga\Module\Setup;
 use ArrayIterator;
 use IteratorAggregate;
 use Icinga\Module\Setup\Exception\SetupException;
+use Traversable;
 
 /**
  * Container for multiple configuration steps
@@ -21,7 +22,7 @@ class Setup implements IteratorAggregate
         $this->steps = array();
     }
 
-    public function getIterator()
+    public function getIterator(): Traversable
     {
         return new ArrayIterator($this->getSteps());
     }