diff --git a/src/Foundation/AbstractDao.php b/src/Foundation/AbstractDao.php
index b62b4cf..36f708e 100644
--- a/src/Foundation/AbstractDao.php
+++ b/src/Foundation/AbstractDao.php
@@ -423,7 +423,7 @@ public function getId($forceArray = false)
    * @return mixed data which can be serialized by <b>json_encode</b>,
    * which is a value of any type other than a resource.
    */
-  public function jsonSerialize()
+  public function jsonSerialize(): mixed
   {
     return Objects::propertyValues($this);
   }