diff --git a/authserv/ldap_model.py b/authserv/ldap_model.py
index a3f73583f94c80fe509563e64447480b90abc91b..49c827fad1327b89d5030459ec333ceb5d0bf0d7 100644
--- a/authserv/ldap_model.py
+++ b/authserv/ldap_model.py
@@ -57,7 +57,7 @@ class UserDb(model.UserDb):
             #
             if 'dn' in ldap_params:
                 base = ldap_params['dn'].replace('%s', escape_dn_chars(username))
-                filt = ldap_params.get('filter', '').replace('%s', escape_filter_chars(username))
+                filt = ldap_params.get('filter', '(objectClass=*)').replace('%s', escape_filter_chars(username))
                 scope = ldap.SCOPE_BASE
             else:
                 base = ldap_params['base'].replace('%s', escape_dn_chars(username))