diff --git a/core/lib/Drupal/Core/EventSubscriber/DefaultExceptionHtmlSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/DefaultExceptionHtmlSubscriber.php
index 38cb895..b6b2b09 100644
--- a/core/lib/Drupal/Core/EventSubscriber/DefaultExceptionHtmlSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/DefaultExceptionHtmlSubscriber.php
@@ -137,9 +137,12 @@ protected function makeSubrequest(GetResponseForExceptionEvent $event, $url, $st
       // The routing to the 404 page should be done as GET request because it is
       // restricted to GET and POST requests only. Otherwise a DELETE request
       // would for example trigger a method not allowed exception.
-      $request_context = clone ($this->accessUnawareRouter->getContext());
-      $request_context->setMethod('GET');
-      $this->accessUnawareRouter->setContext($request_context);
+      $original_request_context = $this->accessUnawareRouter->getContext();
+      if ($original_request_context) {
+        $request_context = clone $original_request_context;
+        $request_context->setMethod('GET');
+        $this->accessUnawareRouter->setContext($request_context);
+      }
 
       $sub_request->attributes->add($this->accessUnawareRouter->match($url));