diff --git a/Tests/Fixtures/FooInterfaceDummyDenormalizer.php b/Tests/Fixtures/FooInterfaceDummyDenormalizer.php
index a8c45373..0fa3c820 100644
--- a/Tests/Fixtures/FooInterfaceDummyDenormalizer.php
+++ b/Tests/Fixtures/FooInterfaceDummyDenormalizer.php
@@ -15,7 +15,7 @@
 
 final class FooInterfaceDummyDenormalizer implements DenormalizerInterface
 {
-    public function denormalize(mixed $data, string $type, string $format = null, array $context = []): array
+    public function denormalize(mixed $data, string $type, ?string $format = null, array $context = []): array
     {
         $result = [];
         foreach ($data as $foo) {
@@ -27,7 +27,7 @@ public function denormalize(mixed $data, string $type, string $format = null, ar
         return $result;
     }
 
-    public function supportsDenormalization(mixed $data, string $type, string $format = null, array $context = []): bool
+    public function supportsDenormalization(mixed $data, string $type, ?string $format = null, array $context = []): bool
     {
         if (str_ends_with($type, '[]')) {
             $className = substr($type, 0, -2);
diff --git a/Tests/Fixtures/StaticConstructorNormalizer.php b/Tests/Fixtures/StaticConstructorNormalizer.php
index c2e77aa4..1ba6884b 100644
--- a/Tests/Fixtures/StaticConstructorNormalizer.php
+++ b/Tests/Fixtures/StaticConstructorNormalizer.php
@@ -23,17 +23,17 @@ public function getSupportedTypes(?string $format): array
         return [StaticConstructorDummy::class];
     }
 
-    protected function extractAttributes(object $object, string $format = null, array $context = []): array
+    protected function extractAttributes(object $object, ?string $format = null, array $context = []): array
     {
         return get_object_vars($object);
     }
 
-    protected function getAttributeValue(object $object, string $attribute, string $format = null, array $context = []): mixed
+    protected function getAttributeValue(object $object, string $attribute, ?string $format = null, array $context = []): mixed
     {
         return $object->$attribute;
     }
 
-    protected function setAttributeValue(object $object, string $attribute, mixed $value, string $format = null, array $context = []): void
+    protected function setAttributeValue(object $object, string $attribute, mixed $value, ?string $format = null, array $context = []): void
     {
         $object->$attribute = $value;
     }