diff --git c/core/modules/system/lib/Drupal/system/Tests/Datetime/DrupalDateTimeTest.php w/core/modules/system/lib/Drupal/system/Tests/Datetime/DrupalDateTimeTest.php
index 0d8571a..3707bf8 100644
--- c/core/modules/system/lib/Drupal/system/Tests/Datetime/DrupalDateTimeTest.php
+++ w/core/modules/system/lib/Drupal/system/Tests/Datetime/DrupalDateTimeTest.php
@@ -40,8 +40,13 @@ public function setUp() {
    * Test that the AJAX Timezone Callback can deal with various formats.
    */
   public function testSystemTimezone() {
+    $options = array(
+      'query' => array(
+        'date' => 'Tue+Sep+17+2013+21%3A35%3A31+GMT%2B0100+(BST)#',
+      )
+    );
     // Query the AJAX Timezone Callback with a long-format date.
-    $response = $this->drupalGet('system/timezone/BST/3600/1?date=Tue+Sep+17+2013+21%3A35%3A31+GMT%2B0100+(BST)#');
+    $response = $this->drupalGet('system/timezone/BST/3600/1', $options);
     $this->assertEqual($response, '"Europe\/London"', 'Timezone AJAX callback successfully identifies and responds to a long-format date.');
   }