diff --git a/core/modules/system/lib/Drupal/system/Controller/SystemController.php b/core/modules/system/lib/Drupal/system/Controller/SystemController.php
index 283a942..094123b 100644
--- a/core/modules/system/lib/Drupal/system/Controller/SystemController.php
+++ b/core/modules/system/lib/Drupal/system/Controller/SystemController.php
@@ -50,6 +50,8 @@ class SystemController extends ControllerBase implements ContainerInjectionInter
   protected $formBuilder;
 
   /**
+   * The theme handler service.
+   *
    * @var \Drupal\Core\Extension\ThemeHandlerInterface
    */
   protected $themeHandler;