diff --git a/core/lib/Drupal/Core/Theme/Registry.php b/core/lib/Drupal/Core/Theme/Registry.php
index 940716af77770fba217eaa8b64713e973e078c00..c46f9109e7fd617d56fdbf5355fe8dc6d1c6bf45 100644
--- a/core/lib/Drupal/Core/Theme/Registry.php
+++ b/core/lib/Drupal/Core/Theme/Registry.php
@@ -134,6 +134,13 @@ class Registry implements DestructableInterface {
    */
   protected $themeHandler;
 
+  /**
+   * The theme initialization.
+   *
+   * @var \Drupal\Core\Theme\ThemeInitializationInterface
+   */
+  protected $themeInitialization;
+
   /**
    * The theme manager.
    *