diff --git a/core/modules/field_ui/lib/Drupal/field_ui/Access/FormModeAccessCheck.php b/core/modules/field_ui/lib/Drupal/field_ui/Access/FormModeAccessCheck.php
index 92e3790..07cde56 100644
--- a/core/modules/field_ui/lib/Drupal/field_ui/Access/FormModeAccessCheck.php
+++ b/core/modules/field_ui/lib/Drupal/field_ui/Access/FormModeAccessCheck.php
@@ -47,6 +47,8 @@ public function access(Route $route, Request $request, AccountInterface $account
         return $account->hasPermission($permission) ? static::ALLOW : static::DENY;
       }
     }
+
+    return static::DENY;
   }
 
 }