diff --git a/UI/WebServerResources/SOGoRootPage.js b/UI/WebServerResources/SOGoRootPage.js
index b6ea6be28..14b834ab5 100644
--- a/UI/WebServerResources/SOGoRootPage.js
+++ b/UI/WebServerResources/SOGoRootPage.js
@@ -20,7 +20,8 @@ function onLoginClick(event) {
   var password = $("password").value;
 
   if (userName.length > 0) {
-    if (loginSuffix && loginSuffix.length > 0
+    if (typeof(loginSuffix) != "undefined"
+	&& loginSuffix.length > 0
 	&& !userName.endsWith(loginSuffix))
       userName += loginSuffix;
     var url = $("connectForm").getAttribute("action");
@@ -39,7 +40,7 @@ function onLoginCallback(http) {
   if (http.readyState == 4) {
     if (isHttpStatus204(http.status)) {
       var userName = $("userName").value;
-      if (loginSuffix
+      if (typeof(loginSuffix) != "undefined"
 	  && loginSuffix.length > 0
 	  && !userName.endsWith(loginSuffix))
 	userName += loginSuffix;