diff --git a/core/modules/system/src/Tests/Theme/TwigRegistryLoaderTest.php b/core/modules/system/src/Tests/Theme/TwigRegistryLoaderTest.php
index 1f32a81..589632b 100644
--- a/core/modules/system/src/Tests/Theme/TwigRegistryLoaderTest.php
+++ b/core/modules/system/src/Tests/Theme/TwigRegistryLoaderTest.php
@@ -59,7 +59,7 @@ public function testTwigNamespaces() {
 
     // Enable a theme that overrides the extend and insert templates to ensure
     // they are picked up by the registry loader.
-    \Drupal::config('system.theme')
+    $this->config('system.theme')
       ->set('default', 'test_theme_twig_registry_loader')
       ->save();
     $this->drupalGet('twig-theme-test/registry-loader');