diff --git a/src/File.php b/src/File.php
index 61dd11a..11e3be6 100755
--- a/src/File.php
+++ b/src/File.php
@@ -43,7 +43,7 @@ public function __construct($id, $name, $hash = null, $size = null, $type = null
     /**
      * @return array
      * */
-    public function jsonSerialize(): mixed
+    public function jsonSerialize()
     {
         return [
             'id'              => $this->getId(),