diff --git a/Models/Session.php b/Models/Session.php
index 5f4c7f3..9d6810d 100755
--- a/Models/Session.php
+++ b/Models/Session.php
@@ -299,7 +299,7 @@ class Session implements \JsonSerializable, ArrayableInterface
     /**
      * {@inheritdoc}
      */
-    public function jsonSerialize()
+    public function jsonSerialize() : mixed
     {
         return $this->toArray();
     }
diff --git a/Models/SessionElement.php b/Models/SessionElement.php
index 9341f61..78d9967 100755
--- a/Models/SessionElement.php
+++ b/Models/SessionElement.php
@@ -126,7 +126,7 @@ class SessionElement implements \JsonSerializable, ArrayableInterface
     /**
      * {@inheritdoc}
      */
-    public function jsonSerialize()
+    public function jsonSerialize() : mixed
     {
         return $this->toArray();
     }