diff --git a/core/lib/Drupal/Core/Template/TwigExtension.php b/core/lib/Drupal/Core/Template/TwigExtension.php
index 897d954d24..60a9bd4c2e 100644
--- a/core/lib/Drupal/Core/Template/TwigExtension.php
+++ b/core/lib/Drupal/Core/Template/TwigExtension.php
@@ -647,7 +647,7 @@ public function createAttribute(array $attributes = []) {
    *   The filtered renderable array.
    */
   public function withoutFilter($element) {
-    if ($element instanceof ArrayAccess) {
+    if ($element instanceof \ArrayAccess) {
       $filtered_element = clone $element;
     }
     else {
diff --git a/core/tests/Drupal/KernelTests/Core/Theme/TwigWhiteListTest.php b/core/tests/Drupal/KernelTests/Core/Theme/TwigWhiteListTest.php
index 7af10f5946..5b11298d69 100644
--- a/core/tests/Drupal/KernelTests/Core/Theme/TwigWhiteListTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Theme/TwigWhiteListTest.php
@@ -113,6 +113,9 @@ protected function setUp() {
    * Tests white-listing of methods doesn't interfere with chaining.
    */
   public function testWhiteListChaining() {
+    // Include the Twig engine so we can call twig_render_template().
+    require_once $this->root . '/core/themes/engines/twig/twig.engine';
+
     $node = Node::create([
       'type' => 'page',
       'title' => 'Some node mmk',