diff -u b/core/lib/Drupal/Core/EventSubscriber/HttpExceptionSubscriberBase.php b/core/lib/Drupal/Core/EventSubscriber/HttpExceptionSubscriberBase.php
--- b/core/lib/Drupal/Core/EventSubscriber/HttpExceptionSubscriberBase.php
+++ b/core/lib/Drupal/Core/EventSubscriber/HttpExceptionSubscriberBase.php
@@ -100,7 +100,7 @@
       $method = 'on' . $exception->getStatusCode();
       // Keep just the leading number of the status code to produce either a
       // on400 or a 500 method callback.
-      $method_fallback = 'on' . floor($exception->getStatusCode() / 100) . 'xx';
+      $method_fallback = 'on' . strval($exception->getStatusCode())[0] . 'xx';
       // We want to allow the method to be called and still not set a response
       // if it has additional filtering logic to determine when it will apply.
       // It is therefore the method's responsibility to set the response on the