diff --git a/lam/lib/account.inc b/lam/lib/account.inc
index a8ff766b..1a799b4d 100644
--- a/lam/lib/account.inc
+++ b/lam/lib/account.inc
@@ -434,6 +434,10 @@ function get_preg($argument, $regexp) {
 		case 'username':	// first character must be a letter. All letters, numbers, space and ._- are allowed characters
 					$pregexpr = '/^[[:alpha:]]([[:alnum:]\\.\\ \\_-])*$/';
 					break;
+		case 'usernameList':	// comma separated list of user names
+		case 'groupnameList':	// comma separated list of group names
+					$pregexpr = '[[:alpha:]]([[:alnum:]\\.\\ \\_-])(,[[:alpha:]]([[:alnum:]\\.\\ \\_-]))*';
+					break;
 		case 'hostname':	// first character must be letter, last must be $. Only normal letters, numbers and ._- are allowed
 					$pregexpr = '/^[a-zA-Z]([a-zA-Z0-9\\.\\_-])*\\$$/';
 					break;