diff --git a/core/modules/block/lib/Drupal/block/Controller/BlockAutocompleteController.php b/core/modules/block/lib/Drupal/block/Controller/BlockAutocompleteController.php
index 539a8c1..173b051 100644
--- a/core/modules/block/lib/Drupal/block/Controller/BlockAutocompleteController.php
+++ b/core/modules/block/lib/Drupal/block/Controller/BlockAutocompleteController.php
@@ -75,4 +75,18 @@ public function autocomplete(Request $request) {
     return new JsonResponse($matches);
   }
 
+  /**
+   * Sets whether the admin menu is in compact mode or not.
+   *
+   * @param string $mode
+   *   Valid values are 'on' and 'off'.
+   *
+   * @return \Symfony\Component\HttpFoundation\RedirectResponse
+   *   A redirect response. Redirects back to the front page.
+   */
+  public function compactPage($mode) {
+    user_cookie_save(array('admin_compact_mode' => ($mode == 'on')));
+    return new RedirectResponse(url('<front>', array('absolute' => TRUE)));
+  }
+
 }
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 1935f5c..870ad56 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -631,13 +631,6 @@ function system_menu() {
     'menu_name' => 'admin',
     'file' => 'system.admin.inc',
   );
-  $items['admin/compact'] = array(
-    'title' => 'Compact mode',
-    'page callback' => 'system_admin_compact_page',
-    'access arguments' => array('access administration pages'),
-    'type' => MENU_CALLBACK,
-    'file' => 'system.admin.inc',
-  );
   $items['admin/tasks'] = array(
     'title' => 'Tasks',
     'type' => MENU_DEFAULT_LOCAL_TASK,
@@ -2995,14 +2988,14 @@ function confirm_form($form, $question, $path, $description = NULL, $yes = NULL,
  * such as the configuration page and the permissions page.
  *
  * Whether the user is in compact mode is determined by a cookie, which is set
- * for the user by system_admin_compact_page().
+ * for the user by \Drupal\system\Controller\SystemController::compactPage().
  *
  * If the user does not have the cookie, the default value is given by the
  * system variable 'admin_compact_mode', which itself defaults to FALSE. This
  * does not have a user interface to set it: it is a hidden variable which can
  * be set in the settings.php file.
  *
- * @return
+ * @return bool
  *   TRUE when in compact mode, FALSE when in expanded mode.
  */
 function system_admin_compact_mode() {
@@ -3012,17 +3005,6 @@ function system_admin_compact_mode() {
 }
 
 /**
- * Menu callback; Sets whether the admin menu is in compact mode or not.
- *
- * @param $mode
- *   Valid values are 'on' and 'off'.
- */
-function system_admin_compact_page($mode = 'off') {
-  user_cookie_save(array('admin_compact_mode' => ($mode == 'on')));
-  return new RedirectResponse(url('<front>', array('absolute' => TRUE)));
-}
-
-/**
  * Generate a list of tasks offered by a specified module.
  *
  * @param $module
diff --git a/core/modules/system/system.routing.yml b/core/modules/system/system.routing.yml
index 017d486..254bf01 100644
--- a/core/modules/system/system.routing.yml
+++ b/core/modules/system/system.routing.yml
@@ -10,6 +10,15 @@ system.cron:
     _controller: '\Drupal\system\CronController::run'
   requirements:
     _access_system_cron: 'TRUE'
+
+system_admin_compact_page:
+  pattern: '/admin/compact/{mode}'
+  defaults:
+    _controller: 'Drupal\system\Controller\SystemController::compactPage'
+    mode: 'off'
+  requirements:
+    _permission: 'access administration pages'
+
 system.machine_name_transliterate:
   pattern: '/machine_name/transliterate'
   defaults: