diff --git a/core/modules/user/lib/Drupal/user/Plugin/views/argument_default/User.php b/core/modules/user/lib/Drupal/user/Plugin/views/argument_default/User.php
index e1eca53..91b44c9 100644
--- a/core/modules/user/lib/Drupal/user/Plugin/views/argument_default/User.php
+++ b/core/modules/user/lib/Drupal/user/Plugin/views/argument_default/User.php
@@ -10,6 +10,8 @@
 use Drupal\views\Plugin\views\argument_default\ArgumentDefaultPluginBase;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Symfony\Component\HttpFoundation\Request;
+use Drupal\user\UserInterface;
+use Drupal\node\NodeInterface;
 
 /**
  * Default argument plugin to extract a user via menu_get_object.
@@ -87,13 +89,17 @@ public function getArgument() {
     // If there is a user object in the current route.
     if ($this->request->attributes->has('user')) {
       $user = $this->request->attributes->get('user');
-      return $user->id();
+      if ($user instanceof UserInterface) {
+        return $user->id();
+      }
     }
 
     // If option to use node author; and node in current route.
     if (!empty($this->options['user']) && $this->request->attributes->has('node')) {
       $node = $this->request->attributes->get('node');
-      return $node->getAuthorId();
+      if ($node instanceof NodeInterface) {
+        return $node->getAuthorId();
+      }
     }
 
     // If the current page is a view that takes uid as an argument.