diff --git a/gluon/tools.py b/gluon/tools.py
index 131b7a8e..0dbecb1e 100644
--- a/gluon/tools.py
+++ b/gluon/tools.py
@@ -2112,7 +2112,7 @@ class Auth(object):
         success = False
         if row:
             userfield = self.settings.login_userfield or 'username' \
-                if 'username' in table_user.fields else 'email'
+                if 'username' in table.fields else 'email'
             # If ticket is a service Ticket and RENEW flag respected
             if ticket[0:3] == 'ST-' and \
                     not ((row.renew and renew) ^ renew):