diff --git a/core/lib/Drupal/Core/Access/RouteProcessorCsrf.php b/core/lib/Drupal/Core/Access/RouteProcessorCsrf.php
index 7121f57..11be637 100644
--- a/core/lib/Drupal/Core/Access/RouteProcessorCsrf.php
+++ b/core/lib/Drupal/Core/Access/RouteProcessorCsrf.php
@@ -72,6 +72,7 @@ public function onRouteAlter(RouteBuildEvent $event) {
    */
   public static function getSubscribedEvents() {
     $events[RoutingEvents::ALTER][] = ['onRouteAlter', -1000];
+    return $events;
   }
 
 }