Index: django/contrib/admin/views/decorators.py
===================================================================
--- django/contrib/admin/views/decorators.py	(revision 7535)
+++ django/contrib/admin/views/decorators.py	(working copy)
@@ -85,14 +85,8 @@
             if '@' in username:
                 # Mistakenly entered e-mail address instead of username? Look it up.
                 try:
-                    users = list(User.objects.filter(email=username))
-                    if len(users) == 1:
-                        user = users[0]
-                    else:
-                        # Either we cannot find the user, or if more than 1 
-                        # we cannot guess which user is the correct one.
-                        raise User.DoesNotExist()                        
-                except User.DoesNotExist:
+                    user = User.objects.get(email=username)
+                except (User.DoesNotExist, AssertionError):
                     message = _("Usernames cannot contain the '@' character.")
                 else:
                     message = _("Your e-mail address is not your username. Try '%s' instead.") % user.username