diff --git a/src/Elasticsearch/Serializer/ItemNormalizer.php b/src/Elasticsearch/Serializer/ItemNormalizer.php
index ecf4aafbb3a..f88d1637d66 100644
--- a/src/Elasticsearch/Serializer/ItemNormalizer.php
+++ b/src/Elasticsearch/Serializer/ItemNormalizer.php
@@ -28,6 +28,8 @@
  */
 final class ItemNormalizer implements NormalizerInterface, DenormalizerInterface, SerializerAwareInterface, CacheableSupportsMethodInterface
 {
+    public const FORMAT = 'elasticsearch';
+
     private $decorated;
 
     public function __construct(NormalizerInterface $decorated)