diff --git a/core/modules/menu/menu.module b/core/modules/menu/menu.module
index 189c479..b3d12d6 100644
--- a/core/modules/menu/menu.module
+++ b/core/modules/menu/menu.module
@@ -209,12 +209,16 @@ function menu_menu_predelete(Menu $menu) {
   menu_delete_links($menu->id());
 
   // Remove menu from active menus variable.
-  $active_menus = variable_get('menu_default_active_menus', array_keys(menu_get_menus()));
-  foreach ($active_menus as $i => $menu_name) {
-    if ($menu->id() == $menu_name) {
-      unset($active_menus[$i]);
-      variable_set('menu_default_active_menus', $active_menus);
-    }
+  $config = \Drupal::config('system.menu');
+  $active_menus = $config->get('active_menus_default') ?: array_keys(menu_get_menus());
+  if (in_array($menu->id(), $active_menus)) {
+    $active_menus = array_diff($active_menus, array($menu->id()));
+    // Prevent the gap left by the removed menu from causing array indices to
+    // be saved.
+    $active_menus = array_values($active_menus);
+    $config
+      ->set('active_menus_default', $active_menus)
+      ->save();
   }
 }
 
diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index 1bfc0b2..42ced4c 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -1764,7 +1764,7 @@ function system_update_8032() {
  */
 function system_update_8033() {
   update_variables_to_config('system.menu', array(
-    'active_menus_default' => 'active_menus_default'
+    'menu_default_active_menus' => 'active_menus_default'
   ));
 }