diff --git a/functions.inc.php b/functions.inc.php
index 6686b0f9..2161e2c2 100644
--- a/functions.inc.php
+++ b/functions.inc.php
@@ -224,7 +224,7 @@ function language_selector() {
  * @todo skip DNS check if the domain exists in PostfixAdmin?
  */
 function check_domain($domain) {
-    if (!preg_match('/^([-0-9A-Z]+\.)+' . '([-0-9A-Z]){2,13}$/i', ($domain))) {
+    if (!preg_match('/^([-0-9A-Z]+\.)+' . '([-0-9A-Z]){1,13}$/i', ($domain))) {
         return sprintf(Config::lang('pInvalidDomainRegex'), htmlentities($domain));
     }