diff --git a/core/lib/Drupal/Core/Theme/Registry.php b/core/lib/Drupal/Core/Theme/Registry.php
index 0167a74..9a9d8f6 100644
--- a/core/lib/Drupal/Core/Theme/Registry.php
+++ b/core/lib/Drupal/Core/Theme/Registry.php
@@ -18,6 +18,8 @@
 /**
  * Defines the theme registry service.
  *
+ * @internal
+ *
  * @todo Replace local $registry variables in methods with $this->registry.
  */
 class Registry implements DestructableInterface {