--- backends.py.orig	2011-06-15 09:24:52.000000000 +0200
+++ backends.py	2011-06-15 09:25:39.000000000 +0200
@@ -17,6 +17,8 @@
             user = User.objects.get(username=username)
             if user.check_password(password):
                 return user
+        except ValueError:
+            return None
         except User.DoesNotExist:
             return None