diff --git a/twig/AdminTwigExtension.php b/twig/AdminTwigExtension.php
index 09ac2e46..cfa99f57 100644
--- a/twig/AdminTwigExtension.php
+++ b/twig/AdminTwigExtension.php
@@ -3,4 +3,5 @@
 
 require_once __DIR__ . '/../classes/plugin/Twig/AdminTwigExtension.php';
 
+user_error("require_once('user/plugins/admin/twig/AdminTwigExtension.php') is deprecated. All admin classes are using composer autoloader.", E_USER_DEPRECATED);
 class_alias('Grav\Plugin\Admin\Twig\AdminTwigExtension', 'Grav\Plugin\Admin\AdminTwigExtension');