diff --git a/src/Concerns/To.php b/src/Concerns/To.php
index 9c7ee49..10644f6 100644
--- a/src/Concerns/To.php
+++ b/src/Concerns/To.php
@@ -6,7 +6,7 @@
 
 trait To
 {
-    public function toJson($flags = JSON_UNESCAPED_UNICODE): string
+    public function toJson(int $flags = JSON_UNESCAPED_UNICODE): string
     {
         return json_encode($this->toArray(), $flags);
     }