diff --git a/src/Record.php b/src/Record.php
index fbaa117..f324c28 100644
--- a/src/Record.php
+++ b/src/Record.php
@@ -219,7 +219,7 @@ public function getId()
      *
      * @return array
      */
-    public function jsonSerialize()
+    public function jsonSerialize(): array|string
     {
         $o = [];
         foreach ($this->properties as $prop) {