diff --git a/tests/src/Functional/TwigTweakTest.php b/tests/src/Functional/TwigTweakTest.php
index 4e4f24e..553f3d9 100644
--- a/tests/src/Functional/TwigTweakTest.php
+++ b/tests/src/Functional/TwigTweakTest.php
@@ -22,6 +22,11 @@ class TwigTweakTest extends BrowserTestBase {
 
   use TestFileCreationTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */