diff --git a/core/includes/common.inc b/core/includes/common.inc
index 86fc44a..18f4087 100644
--- a/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -4911,21 +4911,6 @@ function _drupal_bootstrap_full($skip = FALSE) {
   // Initialize language (which can strip path prefix) prior to initializing
   // current_path().
   drupal_language_initialize();
-
-  // Let all modules take action before the menu system handles the request.
-  // We do not want this while running update.php.
-  if (!defined('MAINTENANCE_MODE') || MAINTENANCE_MODE != 'update') {
-    // Prior to invoking hook_init(), initialize the theme (potentially a custom
-    // one for this page), so that:
-    // - Modules with hook_init() implementations that call theme() or
-    //   theme_get_registry() don't initialize the incorrect theme.
-    // - The theme can have hook_*_alter() implementations affect page building
-    //   (e.g., hook_form_alter(), hook_node_view_alter(), hook_page_alter()),
-    //   ahead of when rendering starts.
-    menu_set_custom_theme();
-    drupal_theme_initialize();
-    module_invoke_all('init');
-  }
 }
 
 /**
diff --git a/core/lib/Drupal/Core/EventSubscriber/LegacyRequestSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/LegacyRequestSubscriber.php
index 242f935..889ca0a 100644
--- a/core/lib/Drupal/Core/EventSubscriber/LegacyRequestSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/LegacyRequestSubscriber.php
@@ -13,35 +13,24 @@
 use Symfony\Component\EventDispatcher\EventSubscriberInterface;
 
 /**
- * KernelEvents::REQUEST event subscriber to initialize theme and modules.
+ * KernelEvents::REQUEST event subscriber to inform Drupal that it is fully bootstrapped.
  *
  * @todo Remove this subscriber when all of the code in it has been refactored.
  */
 class LegacyRequestSubscriber implements EventSubscriberInterface {
 
   /**
-   * Initializes the rest of the legacy Drupal subsystems.
+   * Informs Drupal that it is fully bootstrapped.
    *
    * @param Symfony\Component\HttpKernel\Event\GetResponseEvent $event
    *   The Event to process.
    */
   public function onKernelRequestLegacy(GetResponseEvent $event) {
     if ($event->getRequestType() == HttpKernelInterface::MASTER_REQUEST) {
-      // Prior to invoking hook_init(), initialize the theme (potentially a
-      // custom one for this page), so that:
-      // - Modules with hook_init() implementations that call theme() or
-      //   theme_get_registry() don't initialize the incorrect theme.
-      // - The theme can have hook_*_alter() implementations affect page
-      //   building (e.g., hook_form_alter(), hook_node_view_alter(),
-      //   hook_page_alter()), ahead of when rendering starts.
-      menu_set_custom_theme();
-      drupal_theme_initialize();
-      module_invoke_all('init');
-
       // Tell Drupal it is now fully bootstrapped (for the benefit of code that
       // calls drupal_get_bootstrap_phase()), but without having
       // _drupal_bootstrap_full() do anything, since we've already done the
-      // equivalent above and in earlier listeners.
+      // equivalent in earlier listeners.
       _drupal_bootstrap_full(TRUE);
       drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);
     }
diff --git a/core/lib/Drupal/Core/HtmlPageController.php b/core/lib/Drupal/Core/HtmlPageController.php
index ab9af59..793fa4b 100644
--- a/core/lib/Drupal/Core/HtmlPageController.php
+++ b/core/lib/Drupal/Core/HtmlPageController.php
@@ -46,6 +46,16 @@ public function setContainer(ContainerInterface $container = NULL) {
    *   A response object.
    */
   public function content(Request $request, $_content) {
+    // Prior to invoking hook_init(), initialize the theme (potentially a
+    // custom one for this page), so that:
+    // - Modules with hook_init() implementations that call theme() or
+    //   theme_get_registry() don't initialize the incorrect theme.
+    // - The theme can have hook_*_alter() implementations affect page
+    //   building (e.g., hook_form_alter(), hook_node_view_alter(),
+    //   hook_page_alter()), ahead of when rendering starts.
+    menu_set_custom_theme();
+    drupal_theme_initialize();
+    module_invoke_all('init');
 
     // @todo When we have a Generator, we can replace the forward() call with
     // a render() call, which would handle ESI and hInclude as well.  That will