diff --git a/lam/lib/account.inc b/lam/lib/account.inc
index dc802ba5..805b00cb 100644
--- a/lam/lib/account.inc
+++ b/lam/lib/account.inc
@@ -491,6 +491,9 @@ function get_preg($argument, $regexp) {
 		case 'date':
 					$pregexpr = '/^((0[1-9])|([1-2][0-9])|30|31)\\-((0[1-9])|(1[0-2]))\\-[1-3][0-9][0-9][0-9]$/';
 					break;
+		case 'sambaLogonHours':
+					$pregexpr = '/^[0-9a-fA-F]{42}$/';
+					break;
 	}
 	if ($pregexpr!='')
 		if (preg_match($pregexpr, $argument)) {