diff -u b/core/modules/simpletest/src/WebTestBase.php b/core/modules/simpletest/src/WebTestBase.php
--- b/core/modules/simpletest/src/WebTestBase.php
+++ b/core/modules/simpletest/src/WebTestBase.php
@@ -782,7 +782,7 @@
     // 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')
+      ->set('timezone.default', 'Etc/UTC')
       ->save();
 
     // Collect modules to install.