diff --git a/core/core.services.yml b/core/core.services.yml
index 51a42bd..3a90788 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -421,7 +421,7 @@ services:
     class: Drupal\Core\Controller\DialogController
     arguments: ['@controller_resolver', '@title_resolver']
   router_listener:
-    class: Symfony\Component\HttpKernel\EventListener\RouterListener
+    class: Drupal\Core\EventSubscriber\RouterListener
     tags:
       - { name: event_subscriber }
     arguments: ['@router']
diff --git a/core/lib/Drupal/Core/EventSubscriber/RouterListener.php b/core/lib/Drupal/Core/EventSubscriber/RouterListener.php
new file mode 100644
index 0000000..f3d76ca
--- /dev/null
+++ b/core/lib/Drupal/Core/EventSubscriber/RouterListener.php
@@ -0,0 +1,32 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\EventSubscriber\RouterListener.
+ */
+
+namespace Drupal\Core\EventSubscriber;
+
+use Drupal\Core\ParamConverter\ParamNotConvertedException;
+use Symfony\Component\HttpKernel\Event\GetResponseEvent;
+use Symfony\Component\HttpKernel\EventListener\RouterListener as SymfonyRouterListener;
+use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
+
+/**
+ * Wraps the upstream request subscriber.
+ */
+class RouterListener extends SymfonyRouterListener {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function onKernelRequest(GetResponseEvent $event) {
+    try {
+      parent::onKernelRequest($event);
+    }
+    catch (ParamNotConvertedException $e) {
+      throw new NotFoundHttpException();
+    }
+  }
+
+}