diff --git a/src/Engine/Utils/Collections/CollectionTrait.php b/src/Engine/Utils/Collections/CollectionTrait.php
index cc85949..70daf0d 100644
--- a/src/Engine/Utils/Collections/CollectionTrait.php
+++ b/src/Engine/Utils/Collections/CollectionTrait.php
@@ -23,6 +23,7 @@ protected function setValues($values)
      * Returns the object to JSON serialize.
      * @return array
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return $this->getArrayCopy();
diff --git a/src/Engine/Utils/Collections/MultivariateFeatureStateValueModelList.php b/src/Engine/Utils/Collections/MultivariateFeatureStateValueModelList.php
index 8edc773..f2926d4 100644
--- a/src/Engine/Utils/Collections/MultivariateFeatureStateValueModelList.php
+++ b/src/Engine/Utils/Collections/MultivariateFeatureStateValueModelList.php
@@ -14,6 +14,7 @@ class MultivariateFeatureStateValueModelList extends \ArrayObject implements \Js
      * Returns the object to JSON serialize.
      * @return array
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         $stateValues = $this->getArrayCopy();