diff --git a/src/Symfony/Component/Serializer/Tests/Fixtures/DenormalizableDummy.php b/src/Symfony/Component/Serializer/Tests/Fixtures/DenormalizableDummy.php
index bbf54bd5f7055..a768a19989c48 100644
--- a/src/Symfony/Component/Serializer/Tests/Fixtures/DenormalizableDummy.php
+++ b/src/Symfony/Component/Serializer/Tests/Fixtures/DenormalizableDummy.php
@@ -16,7 +16,7 @@
 
 class DenormalizableDummy implements DenormalizableInterface
 {
-    public function denormalize(DenormalizerInterface $denormalizer, array|string|int|float|bool $data, string $format = null, array $context = [])
+    public function denormalize(DenormalizerInterface $denormalizer, array|string|int|float|bool $data, string $format = null, array $context = []): void
     {
     }
 }
diff --git a/src/Symfony/Component/Serializer/Tests/Fixtures/NormalizableTraversableDummy.php b/src/Symfony/Component/Serializer/Tests/Fixtures/NormalizableTraversableDummy.php
index 5ee205fd16bea..d6b38b89af1dc 100644
--- a/src/Symfony/Component/Serializer/Tests/Fixtures/NormalizableTraversableDummy.php
+++ b/src/Symfony/Component/Serializer/Tests/Fixtures/NormalizableTraversableDummy.php
@@ -26,11 +26,7 @@ public function normalize(NormalizerInterface $normalizer, string $format = null
         ];
     }
 
-    public function denormalize(DenormalizerInterface $denormalizer, array|string|int|float|bool $data, string $format = null, array $context = [])
+    public function denormalize(DenormalizerInterface $denormalizer, array|string|int|float|bool $data, string $format = null, array $context = []): void
     {
-        return [
-            'foo' => 'denormalizedFoo',
-            'bar' => 'denormalizedBar',
-        ];
     }
 }
diff --git a/src/Symfony/Component/Serializer/Tests/Fixtures/ScalarDummy.php b/src/Symfony/Component/Serializer/Tests/Fixtures/ScalarDummy.php
index 31ca36ab72e42..949407d116b68 100644
--- a/src/Symfony/Component/Serializer/Tests/Fixtures/ScalarDummy.php
+++ b/src/Symfony/Component/Serializer/Tests/Fixtures/ScalarDummy.php
@@ -26,7 +26,7 @@ public function normalize(NormalizerInterface $normalizer, string $format = null
         return 'xml' === $format ? $this->xmlFoo : $this->foo;
     }
 
-    public function denormalize(DenormalizerInterface $denormalizer, array|string|int|float|bool $data, string $format = null, array $context = [])
+    public function denormalize(DenormalizerInterface $denormalizer, array|string|int|float|bool $data, string $format = null, array $context = []): void
     {
         if ('xml' === $format) {
             $this->xmlFoo = $data;