diff --git a/Models/Contract.php b/Models/Contract.php
index dd203d1..c48788d 100755
--- a/Models/Contract.php
+++ b/Models/Contract.php
@@ -158,7 +158,7 @@ class Contract
     /**
      * {@inheritdoc}
      */
-    public function jsonSerialize()
+    public function jsonSerialize() : mixed
     {
         return $this->toArray();
     }
diff --git a/Models/ContractType.php b/Models/ContractType.php
index a3ffad1..b9e2d83 100755
--- a/Models/ContractType.php
+++ b/Models/ContractType.php
@@ -113,7 +113,7 @@ class ContractType implements \JsonSerializable, ArrayableInterface
     /**
      * {@inheritdoc}
      */
-    public function jsonSerialize()
+    public function jsonSerialize() : mixed
     {
         return $this->toArray();
     }
diff --git a/Models/ContractTypeL11n.php b/Models/ContractTypeL11n.php
index 12b6337..2ab8b48 100755
--- a/Models/ContractTypeL11n.php
+++ b/Models/ContractTypeL11n.php
@@ -129,7 +129,7 @@ class ContractTypeL11n implements \JsonSerializable, ArrayableInterface
     /**
      * {@inheritdoc}
      */
-    public function jsonSerialize()
+    public function jsonSerialize() : mixed
     {
         return $this->toArray();
     }