diff --git a/library/Icinga/Application/ApplicationBootstrap.php b/library/Icinga/Application/ApplicationBootstrap.php
index 14e28b3bc..d0330770e 100644
--- a/library/Icinga/Application/ApplicationBootstrap.php
+++ b/library/Icinga/Application/ApplicationBootstrap.php
@@ -344,7 +344,7 @@ abstract class ApplicationBootstrap
      */
     public function setupAutoloader()
     {
-        require $this->libDir . '/Icinga/Application/ClassLoader.php';
+        require_once $this->libDir . '/Icinga/Application/ClassLoader.php';
 
         $this->loader = new ClassLoader();
         $this->loader->registerNamespace('Icinga', $this->libDir . '/Icinga');
diff --git a/library/Icinga/Util/TimezoneDetect.php b/library/Icinga/Util/TimezoneDetect.php
index 9b6bbc8dc..4967c7f57 100644
--- a/library/Icinga/Util/TimezoneDetect.php
+++ b/library/Icinga/Util/TimezoneDetect.php
@@ -3,8 +3,6 @@
 
 namespace Icinga\Util;
 
-use Icinga\Application\Platform;
-
 /**
  * Retrieve timezone information from cookie
  */
@@ -52,19 +50,17 @@ class TimezoneDetect
             return;
         }
 
-        if (Platform::isCli() === false && array_key_exists(self::$cookieName, $_COOKIE)) {
-            $cookieValue = $_COOKIE[self::$cookieName];
-            list($offset, $dst) = explode(
-                strpos($cookieValue, ',') === false ? '-' : ',',
-                $cookieValue
-            );
-            $timezoneName = timezone_name_from_abbr('', (int)$offset, (int)$dst);
+        if (array_key_exists(self::$cookieName, $_COOKIE)) {
+            $matches = array();
+            if (preg_match('/\A(-?\d+)[\-,](\d+)\z/', $_COOKIE[self::$cookieName], $matches)) {
+                $offset = $matches[1];
+                $timezoneName = timezone_name_from_abbr('', (int) $offset, (int) $matches[2]);
 
-            self::$success = (bool)$timezoneName;
-
-            if (self::$success === true) {
-                self::$offset = $offset;
-                self::$timezoneName = $timezoneName;
+                self::$success = (bool) $timezoneName;
+                if (self::$success) {
+                    self::$offset = $offset;
+                    self::$timezoneName = $timezoneName;
+                }
             }
         }
     }
diff --git a/test/php/library/Icinga/Util/TimezoneDetectTest.php b/test/php/library/Icinga/Util/TimezoneDetectTest.php
new file mode 100644
index 000000000..9df04720c
--- /dev/null
+++ b/test/php/library/Icinga/Util/TimezoneDetectTest.php
@@ -0,0 +1,45 @@
+<?php
+/* Icinga Web 2 | (c) 2017 Icinga Development Team | GPLv2+ */
+
+namespace Tests\Icinga\Util;
+
+use Icinga\Test\BaseTestCase;
+use Icinga\Util\TimezoneDetect;
+
+class TimezoneDetectTest extends BaseTestCase
+{
+    public function testPositiveTimezoneOffsetSeparatedByComma()
+    {
+        $this->assertTimezoneDetection('3600,0', 'Europe/Paris');
+    }
+
+    public function testPositiveTimezoneOffsetSeparatedByHyphen()
+    {
+        $this->assertTimezoneDetection('3600-0', 'Europe/Paris');
+    }
+
+    public function testNegativeTimezoneOffsetSeparatedByComma()
+    {
+        $this->assertTimezoneDetection('-3600,0', 'Atlantic/Azores');
+    }
+
+    public function testNegativeTimezoneOffsetSeparatedByHyphen()
+    {
+        $this->assertTimezoneDetection('-3600-0', 'Atlantic/Azores');
+    }
+
+    protected function assertTimezoneDetection($cookieValue, $expectedTimezoneName)
+    {
+        $tzDetect = new TimezoneDetect();
+        $tzDetect->reset();
+
+        $_COOKIE[TimezoneDetect::$cookieName] = $cookieValue;
+        $tzDetect = new TimezoneDetect();
+        $this->assertSame(
+            $tzDetect->getTimezoneName(),
+            $expectedTimezoneName,
+            'Failed asserting that the timezone "' . $expectedTimezoneName
+            . '" is being detected from the cookie value "' . $cookieValue . '"'
+        );
+    }
+}