diff --git a/cgi-bin/lconline/check.js b/cgi-bin/lconline/check.js
index 7cd33665..9ead75d7 100644
--- a/cgi-bin/lconline/check.js
+++ b/cgi-bin/lconline/check.js
@@ -17,6 +17,6 @@ function isValid (thisForm) {
 
 // check url syntax
 function checkSyntax (url) {
-    var syntax = /^https?:\/\/[-a-zA-Z.\/=%?~]+$/;
+    var syntax = /^https?:\/\/[-_a-zA-Z0-9.\/=%?~]+$/;
     return syntax.test(url);
 }