diff --git a/src/Symfony/Component/Serializer/Extractor/ObjectPropertyListExtractor.php b/src/Symfony/Component/Serializer/Extractor/ObjectPropertyListExtractor.php
index 8424a2ae730df..922094f8cb45a 100644
--- a/src/Symfony/Component/Serializer/Extractor/ObjectPropertyListExtractor.php
+++ b/src/Symfony/Component/Serializer/Extractor/ObjectPropertyListExtractor.php
@@ -30,7 +30,7 @@ public function __construct(PropertyListExtractorInterface $propertyListExtracto
     /**
      * {@inheritdoc}
      */
-    public function getProperties($object, array $context = [])
+    public function getProperties($object, array $context = []): ?array
     {
         $class = $this->objectClassResolver ? ($this->objectClassResolver)($object) : \get_class($object);
 
diff --git a/src/Symfony/Component/Serializer/Extractor/ObjectPropertyListExtractorInterface.php b/src/Symfony/Component/Serializer/Extractor/ObjectPropertyListExtractorInterface.php
index d422e79f82b84..1dd9b8b99a7d3 100644
--- a/src/Symfony/Component/Serializer/Extractor/ObjectPropertyListExtractorInterface.php
+++ b/src/Symfony/Component/Serializer/Extractor/ObjectPropertyListExtractorInterface.php
@@ -20,9 +20,8 @@ interface ObjectPropertyListExtractorInterface
      * Gets the list of properties available for the given object.
      *
      * @param object $object
-     * @param array  $context
      *
      * @return string[]|null
      */
-    public function getProperties($object, array $context = []);
+    public function getProperties($object, array $context = []): ?array;
 }