diff --git a/src/Normalizer/FieldItemNormalizer.php b/src/Normalizer/FieldItemNormalizer.php
index 276652a..1922297 100644
--- a/src/Normalizer/FieldItemNormalizer.php
+++ b/src/Normalizer/FieldItemNormalizer.php
@@ -138,7 +138,7 @@ public function normalize($field_item, $format = NULL, array $context = []): arr
   /**
    * {@inheritdoc}
    */
-  public function denormalize($data, $class, $format = NULL, array $context = []) {
+  public function denormalize(mixed $data, string $class, ?string $format = NULL, array $context = []) : mixed {
 
     if (!isset($context['target_instance'])) {
       throw new InvalidArgumentException('$context[\'target_instance\'] must be set to denormalize with the FieldItemNormalizer');
diff --git a/src/Normalizer/FieldNormalizer.php b/src/Normalizer/FieldNormalizer.php
index 39c4d17..96153c3 100644
--- a/src/Normalizer/FieldNormalizer.php
+++ b/src/Normalizer/FieldNormalizer.php
@@ -62,7 +62,7 @@ public function normalize($field, $format = NULL, array $context = []): array|bo
   /**
    * {@inheritdoc}
    */
-  public function denormalize($data, $class, $format = NULL, array $context = []) {
+  public function denormalize(mixed $data, string $class, ?string $format = NULL, array $context = []) : mixed {
 
     if (!isset($context['target_instance'])) {
       throw new InvalidArgumentException('$context[\'target_instance\'] must be set to denormalize with the FieldNormalizer');
diff --git a/src/Normalizer/FileEntityNormalizer.php b/src/Normalizer/FileEntityNormalizer.php
index 5a4d40d..9d7cc74 100644
--- a/src/Normalizer/FileEntityNormalizer.php
+++ b/src/Normalizer/FileEntityNormalizer.php
@@ -79,7 +79,7 @@ public function normalize($entity, $format = NULL, array $context = []): array|b
   /**
    * {@inheritdoc}
    */
-  public function denormalize($data, $class, $format = NULL, array $context = []) {
+  public function denormalize(mixed $data, string $class, ?string $format = NULL, array $context = []) : mixed {
 
     $file_data = (string) $this->httpClient->get($data['uri'][0]['value'])->getBody();
 
diff --git a/src/Normalizer/NormalizerBase.php b/src/Normalizer/NormalizerBase.php
index 65802fb..64c794c 100644
--- a/src/Normalizer/NormalizerBase.php
+++ b/src/Normalizer/NormalizerBase.php
@@ -20,7 +20,7 @@ abstract class NormalizerBase extends SerializationNormalizerBase implements Den
   /**
    * {@inheritdoc}
    */
-  public function supportsNormalization($data, string $format = NULL, array $context = []): bool {
+  public function supportsNormalization(mixed $data, ?string $format = NULL, array $context = []): bool {
 
     return in_array($format, $this->formats) && parent::supportsNormalization($data, $format);
   }
@@ -28,7 +28,7 @@ public function supportsNormalization($data, string $format = NULL, array $conte
   /**
    * {@inheritdoc}
    */
-  public function supportsDenormalization($data, string $type, string $format = NULL, array $context = []): bool {
+  public function supportsDenormalization($data, string $type, ?string $format = NULL, array $context = []): bool {
 
     if (in_array($format, $this->formats) && (class_exists($this->supportedInterfaceOrClass) || interface_exists($this->supportedInterfaceOrClass))) {
       $target = new \ReflectionClass($type);