diff --git a/src/events/MailEvent.php b/src/events/MailEvent.php
index a53d10b58a..3ff8ff5834 100644
--- a/src/events/MailEvent.php
+++ b/src/events/MailEvent.php
@@ -44,5 +44,5 @@ class MailEvent extends CancelableEvent
     /**
      * @var array Order data at the time the email sends.
      */
-    public array $orderData;
+    public ?array $orderData;
 }