diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestVerticalTabsForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestVerticalTabsForm.php
index fbd7160a100..08d106a820a 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestVerticalTabsForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestVerticalTabsForm.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\form_test\Form;
 
+use Drupal\Component\Serialization\Json;
 use Drupal\Core\Form\FormBase;
 use Drupal\Core\Form\FormStateInterface;