diff --git a/core/tests/Drupal/Tests/Core/Entity/EntityTypeTest.php b/core/tests/Drupal/Tests/Core/Entity/EntityTypeTest.php
index 9a153796fc..898dd163d0 100644
--- a/core/tests/Drupal/Tests/Core/Entity/EntityTypeTest.php
+++ b/core/tests/Drupal/Tests/Core/Entity/EntityTypeTest.php
@@ -6,6 +6,7 @@
 use Drupal\Core\Entity\Entity\EntityFormMode;
 use Drupal\Core\Entity\EntityType;
 use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Language\LanguageDefault;
 use Drupal\Core\StringTranslation\TranslatableMarkup;
 use Drupal\Core\StringTranslation\TranslationManager;
 use Drupal\Tests\UnitTestCase;
@@ -515,9 +516,7 @@ public function testIsSubClassOf() {
   public function testIsSerializable() {
     $entity_type = $this->setUpEntityType([]);
 
-    $translation = $this->prophesize(UnserializableTranslationManager::class);
-    $translation->__serialize()->willThrow(\Exception::class);
-    $translation_service = $translation->reveal();
+    $translation_service = new UnserializableTranslationManager(new LanguageDefault([]));
     $translation_service->_serviceId = 'string_translation';
 
     $entity_type->setStringTranslation($translation_service);