diff --git a/core/modules/config_translation/src/Tests/ConfigTranslationUiTest.php b/core/modules/config_translation/src/Tests/ConfigTranslationUiTest.php
index 807307c..afef143 100644
--- a/core/modules/config_translation/src/Tests/ConfigTranslationUiTest.php
+++ b/core/modules/config_translation/src/Tests/ConfigTranslationUiTest.php
@@ -465,8 +465,10 @@ public function testDateFormatTranslation() {
 
       // Formatting the date 8 / 27 / 1985 @ 13:37 EST with pattern D should
       // display "Tue".
-      $formatted_date = format_date(494015820, $id, NULL, NULL, 'fr');
+      $formatted_date = format_date(494015820, $id, NULL, 'Europe/Berlin', 'fr');
       $this->assertEqual($formatted_date, 'Tue', 'Got the right formatted date using the date format translation pattern.');
+      $formatted_date = format_date(494015820, $id, NULL, 'Asia/Tokyo', 'fr');
+      $this->assertEqual($formatted_date, 'Wed', 'Got the right formatted date using the date format translation pattern.');
     }
   }
 
diff --git a/core/modules/simpletest/src/WebTestBase.php b/core/modules/simpletest/src/WebTestBase.php
index 2e8702b..941376b 100644
--- a/core/modules/simpletest/src/WebTestBase.php
+++ b/core/modules/simpletest/src/WebTestBase.php
@@ -779,6 +779,12 @@ protected function setUp() {
       ->set('js.preprocess', FALSE)
       ->save();
 
+    // Set an explicit time zone to not rely on the system one, which may vary
+    // from setup to setup.
+    $config->getEditable('system.date')
+      ->set('timezone.default', 'Asia/Tokyo')
+      ->save();
+
     // Collect modules to install.
     $class = get_class($this);
     $modules = array();