diff -u b/core/modules/system/lib/Drupal/system/Controller/SystemController.php b/core/modules/system/lib/Drupal/system/Controller/SystemController.php
--- b/core/modules/system/lib/Drupal/system/Controller/SystemController.php
+++ b/core/modules/system/lib/Drupal/system/Controller/SystemController.php
@@ -10,8 +10,8 @@
 use Drupal\Core\Controller\ControllerBase;
 use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
 use Drupal\Core\Entity\Query\QueryFactory;
+use Drupal\Core\Form\FormBuilder;
 use Drupal\Core\Theme\ThemeAccessCheck;
-use Drupal\system\Form\ThemeAdminForm;
 use Drupal\Core\Access\CsrfTokenGenerator;
 use Drupal\system\SystemManager;
 use Symfony\Component\DependencyInjection\ContainerInterface;
@@ -51,6 +51,13 @@
   protected $themeAccess;
 
   /**
+   * The form builder service.
+   *
+   * @var \Drupal\Core\Form\FormBuilder
+   */
+  protected $formBuilder;
+
+  /**
    * Constructs a new SystemController.
    *
    * @param \Drupal\system\SystemManager $systemManager
@@ -61,12 +68,15 @@
    *   The token generator service.
    * @param \Drupal\Core\Theme\ThemeAccessCheck $theme_access
    *   The theme access checker service.
+   * @param \Drupal\Core\Form\FormBuilder $form_builder
+   *  The form builder service.
    */
-  public function __construct(SystemManager $systemManager, QueryFactory $queryFactory, CsrfTokenGenerator $token_generator, ThemeAccessCheck $theme_access) {
+  public function __construct(SystemManager $systemManager, QueryFactory $queryFactory, CsrfTokenGenerator $token_generator, ThemeAccessCheck $theme_access, FormBuilder $form_builder) {
     $this->systemManager = $systemManager;
     $this->queryFactory = $queryFactory;
     $this->tokenGenerator = $token_generator;
     $this->themeAccess = $theme_access;
+    $this->formBuilder = $form_builder;
   }
 
   /**
@@ -77,7 +87,8 @@
       $container->get('system.manager'),
       $container->get('entity.query'),
       $container->get('csrf_token'),
-      $container->get('access_check.theme')
+      $container->get('access_check.theme'),
+      $container->get('form_builder')
     );
   }
 
@@ -314,7 +325,7 @@
       '#theme_groups' => $theme_groups,
       '#theme_group_titles' => $theme_group_titles,
     );
-    $build[] = \Drupal::formBuilder()->getForm(new ThemeAdminForm(), $admin_theme_options);
+    $build[] = $this->formBuilder->getForm('Drupal\system\Form\ThemeAdminForm', $admin_theme_options);
 
     return $build;
   }