diff --git a/core/lib/Drupal/Core/Theme/ChainThemeNegotiatorInterface.php b/core/lib/Drupal/Core/Theme/ChainThemeNegotiatorInterface.php
index 59a0c5e..6dcae96 100644
--- a/core/lib/Drupal/Core/Theme/ChainThemeNegotiatorInterface.php
+++ b/core/lib/Drupal/Core/Theme/ChainThemeNegotiatorInterface.php
@@ -4,12 +4,13 @@
  * @file
  * Contains \Drupal\Core\Theme\ChainThemeNegotiatorInterface.
  */
+
 namespace Drupal\Core\Theme;
 
 /**
  * Defines an interface for a chained service which determines the active theme.
  */
-interface ChainThemeNegotiatorInterface {
+interface ChainThemeNegotiatorInterface extends ThemeNegotiatorInterface {
 
   /**
    * Adds a active theme negotiation service.