diff --git a/phpBB/includes/functions_privmsgs.php b/phpBB/includes/functions_privmsgs.php
index c4cbb7ca1e..4c34bc92ca 100644
--- a/phpBB/includes/functions_privmsgs.php
+++ b/phpBB/includes/functions_privmsgs.php
@@ -1380,6 +1380,9 @@ function submit_pm($mode, $subject, &$data, $put_in_outbox = true)
 		}
 	}
 
+	// First of all make sure the subject are having the correct length.
+	$subject = truncate_string($subject);
+
 	$db->sql_transaction('begin');
 
 	$sql = '';