diff --git a/tests/Fixtures/TestBundle/State/DummyDtoInputOutputProvider.php b/tests/Fixtures/TestBundle/State/DummyDtoInputOutputProvider.php
index 0355d49cafb..d9f72c4b5be 100644
--- a/tests/Fixtures/TestBundle/State/DummyDtoInputOutputProvider.php
+++ b/tests/Fixtures/TestBundle/State/DummyDtoInputOutputProvider.php
@@ -19,6 +19,7 @@
 use ApiPlatform\Tests\Fixtures\TestBundle\Dto\Document\OutputDto as OutputDtoDocument;
 use ApiPlatform\Tests\Fixtures\TestBundle\Dto\OutputDto;
 use ApiPlatform\Tests\Fixtures\TestBundle\Entity\DummyDtoInputOutput;
+use Doctrine\Common\Collections\Collection;
 
 final class DummyDtoInputOutputProvider implements ProviderInterface
 {
@@ -38,7 +39,7 @@ public function provide(Operation $operation, array $uriVariables = [], array $c
         $outputDto->id = $data->id;
         $outputDto->baz = $data->num;
         $outputDto->bat = $data->str;
-        $outputDto->relatedDummies = (array) $data->relatedDummies;
+        $outputDto->relatedDummies = $data->relatedDummies instanceof Collection ? $data->relatedDummies : (array) $data->relatedDummies;
 
         return $outputDto;
     }