diff --git a/src/Event.php b/src/Event.php
index f587193..f296f28 100644
--- a/src/Event.php
+++ b/src/Event.php
@@ -87,6 +87,7 @@ class Event implements \JsonSerializable
         'ip' => 'string',
         'idfa' => 'string',
         'adid' => 'string',
+        'user_agent' => 'string',
     ];
 
     /**