diff --git a/library/Icinga/Chart/Unit/CalendarUnit.php b/library/Icinga/Chart/Unit/CalendarUnit.php
index 7ce6a994d..74680c778 100644
--- a/library/Icinga/Chart/Unit/CalendarUnit.php
+++ b/library/Icinga/Chart/Unit/CalendarUnit.php
@@ -124,7 +124,7 @@ class CalendarUnit extends LinearUnit
      *
      * @return int The position of the next tick (between 0 and 100)
      */
-    public function current()
+    public function current(): int
     {
         return 100 * (key($this->labels) / count($this->labels));
     }
@@ -132,7 +132,7 @@ class CalendarUnit extends LinearUnit
     /**
      * Move to next tick
      */
-    public function next()
+    public function next(): void
     {
         next($this->labels);
     }
@@ -142,7 +142,7 @@ class CalendarUnit extends LinearUnit
      *
      * @return string
      */
-    public function key()
+    public function key(): string
     {
         return current($this->labels);
     }
@@ -152,7 +152,7 @@ class CalendarUnit extends LinearUnit
      *
      * @return bool
      */
-    public function valid()
+    public function valid(): bool
     {
         return current($this->labels) !== false;
     }
@@ -160,7 +160,7 @@ class CalendarUnit extends LinearUnit
     /**
      * Rewind the internal array
      */
-    public function rewind()
+    public function rewind(): void
     {
         reset($this->labels);
     }
diff --git a/library/Icinga/Chart/Unit/LogarithmicUnit.php b/library/Icinga/Chart/Unit/LogarithmicUnit.php
index 90cad57d5..70961e22f 100644
--- a/library/Icinga/Chart/Unit/LogarithmicUnit.php
+++ b/library/Icinga/Chart/Unit/LogarithmicUnit.php
@@ -111,7 +111,7 @@ class LogarithmicUnit implements AxisUnit
      *
      * @return int
      */
-    public function current()
+    public function current(): int
     {
         return $this->currentTick * (100 / $this->getTicks());
     }
@@ -119,7 +119,7 @@ class LogarithmicUnit implements AxisUnit
     /**
      * Calculate the next tick and tick value
      */
-    public function next()
+    public function next(): void
     {
         ++ $this->currentTick;
     }
@@ -129,7 +129,7 @@ class LogarithmicUnit implements AxisUnit
      *
      * @return string The label for the current tick
      */
-    public function key()
+    public function key(): string
     {
         $currentBase = $this->currentTick + $this->minExp;
         if (abs($currentBase) > 4) {
@@ -143,7 +143,7 @@ class LogarithmicUnit implements AxisUnit
      *
      * @return bool
      */
-    public function valid()
+    public function valid(): bool
     {
         return $this->currentTick >= 0 && $this->currentTick < $this->getTicks();
     }
@@ -151,7 +151,7 @@ class LogarithmicUnit implements AxisUnit
     /**
      * Reset the current tick and label value
      */
-    public function rewind()
+    public function rewind(): void
     {
         $this->currentTick = 0;
     }