diff --git c/core/modules/system/lib/Drupal/system/Controller/ThemeController.php w/core/modules/system/lib/Drupal/system/Controller/ThemeController.php
index 6f2a1ac..6dda925 100644
--- c/core/modules/system/lib/Drupal/system/Controller/ThemeController.php
+++ w/core/modules/system/lib/Drupal/system/Controller/ThemeController.php
@@ -9,7 +9,6 @@
 
 use Drupal\Core\Controller\ControllerBase;
 use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
-use Drupal\Core\Config\ConfigFactory;
 use Drupal\Core\Access\CsrfTokenGenerator;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Symfony\Component\HttpFoundation\Request;
@@ -21,13 +20,6 @@
 class ThemeController extends ControllerBase implements ContainerInjectionInterface {
 
   /**
-   * The config factory service.
-   *
-   * @var \Drupal\Core\Config\ConfigFactory
-   */
-  protected $configFactory;
-
-  /**
    * The CSRF Token Generator Service.
    *
    * @var \Drupal\Core\Access\CsrfTokenGenerator
@@ -37,13 +29,10 @@ class ThemeController extends ControllerBase implements ContainerInjectionInterf
   /**
    * Constructs a ThemeController object.
    *
-   * @param \Drupal\Core\Config\ConfigFactory $config_factory
-   *   Config Factory Service.
    * @param \Drupal\Core\Access\CsrfTokenGenerator
    *   Token Generator Service.
    */
-  public function __construct(ConfigFactory $config_factory, CsrfTokenGenerator $token_generator) {
-    $this->configFactory = $config_factory;
+  public function __construct(CsrfTokenGenerator $token_generator) {
     $this->tokenGenerator = $token_generator;
   }
 
@@ -71,7 +60,7 @@ public static function create(ContainerInterface $container) {
    *   the token is invalid.
    */
   public function disable(Request $request) {
-    $config = $this->configFactory->get('system.theme');
+    $config = $this->config('system.theme');
     $theme = $request->get('theme');
     $token = $request->get('token');
 
@@ -150,7 +139,7 @@ public function enable(Request $request) {
    *   the token is invalid.
    */
   public function defaultTheme(Request $request) {
-    $config = $this->configFactory->get('system.theme');
+    $config = $this->config('system.theme');
     $theme = $request->query->get('theme');
     $token = $request->query->get('token');
     if (isset($theme) && isset($token) && $this->tokenGenerator->validate($token, 'system-theme-operation-link')) {