diff --git a/dns/dyndns/src/www/services_dyndns_edit.php b/dns/dyndns/src/www/services_dyndns_edit.php
index 5baf4c6fc..14675eff7 100644
--- a/dns/dyndns/src/www/services_dyndns_edit.php
+++ b/dns/dyndns/src/www/services_dyndns_edit.php
@@ -38,7 +38,7 @@ function is_dyndns_username($uname)
 {
     if (!is_string($uname)) {
         return false;
-    } elseif (preg_match("/[^a-z0-9\-.@_:]/i", $uname)) {
+    } elseif (preg_match("/[^a-z0-9\-.@_:+]/i", $uname)) {
         return false;
     } else {
         return true;