diff --git a/core/modules/system/lib/Drupal/system/Controller/ThemeController.php b/core/modules/system/lib/Drupal/system/Controller/ThemeController.php
index d715622..43166f0 100644
--- a/core/modules/system/lib/Drupal/system/Controller/ThemeController.php
+++ b/core/modules/system/lib/Drupal/system/Controller/ThemeController.php
@@ -19,7 +19,7 @@ class ThemeController extends ControllerBase {
 
   /**
    * Disables a theme.
-   * 
+   *
    * @param \Symfony\Component\HttpFoundation\Request $request
    *   A request object containing a theme name and a valid token.
    *
@@ -33,6 +33,7 @@ class ThemeController extends ControllerBase {
   public function disable(Request $request) {
     $theme = $request->get('theme');
     $token = $request->get('token');
+    $config = $this->config('system.theme');
 
     if (isset($theme) && isset($token) && drupal_valid_token($token, 'system-theme-operation-link')) {
       // Get current list of themes.
@@ -41,7 +42,7 @@ public function disable(Request $request) {
       // Check if the specified theme is one recognized by the system.
       if (!empty($themes[$theme])) {
         // Do not disable the default or admin theme.
-        if ($theme === $this->config('system.theme')->get('default') || $theme === $this->config('system.theme')->get('admin')) {
+        if ($theme === $config->get('default') || $theme === $config->get('admin')) {
           drupal_set_message($this->t('%theme is the default theme and cannot be disabled.', array('%theme' => $themes[$theme]->info['name'])), 'error');
         }
         else {
@@ -110,7 +111,7 @@ public function enable(Request $request) {
    */
   public function defaultTheme(Request $request) {
     // Set the page title.
-    drupal_set_title($this->t('Set default theme'));
+    $config = $this->config('system.theme');
 
     $theme = $request->query->get('theme');
     $token = $request->query->get('token');
@@ -126,8 +127,7 @@ public function defaultTheme(Request $request) {
         }
 
         // Set the default theme.
-        $this->config('system.theme')->set('default', $theme)
-          ->save();
+        $config->set('default', $theme)->save();
 
         // Rebuild the menu. This duplicates the menu_router_rebuild() in
         // theme_enable(). However, modules must know the current default theme in
@@ -139,7 +139,7 @@ public function defaultTheme(Request $request) {
 
         // The status message depends on whether an admin theme is currently in use:
         // a value of 0 means the admin theme is set to be the default theme.
-        $admin_theme = $this->config('system.theme')->get('admin');
+        $admin_theme = $config->get('admin');
         if ($admin_theme != 0 && $admin_theme != $theme) {
           drupal_set_message($this->t('Please note that the administration theme is still set to the %admin_theme theme; consequently, the theme on this page remains unchanged. All non-administrative sections of the site, however, will show the selected %selected_theme theme by default.', array(
             '%admin_theme' => $themes[$admin_theme]->info['name'],
diff --git a/core/modules/system/system.routing.yml b/core/modules/system/system.routing.yml
index 9e3171c..cd6c2d6 100644
--- a/core/modules/system/system.routing.yml
+++ b/core/modules/system/system.routing.yml
@@ -317,6 +317,7 @@ system_theme_default:
   pattern: '/admin/appearance/default'
   defaults:
     _controller: 'Drupal\system\Controller\ThemeController::defaultTheme'
+    _title: 'Set default theme'
   requirements:
     _permission: 'administer themes'