diff --git a/src/Jsonq.php b/src/Jsonq.php
index d29143b..e91983f 100644
--- a/src/Jsonq.php
+++ b/src/Jsonq.php
@@ -653,7 +653,7 @@ public function values()
      * @return object|array|bool
      * @throws ConditionNotAllowedException
      */
-    public function chunk($amount, callable $fn = null)
+    public function chunk($amount, ?callable $fn = null)
     {
         $this->prepare();