diff --git a/django/contrib/auth/__init__.py b/django/contrib/auth/__init__.py
index 2150893022..1c821801ef 100644
--- a/django/contrib/auth/__init__.py
+++ b/django/contrib/auth/__init__.py
@@ -38,7 +38,7 @@ def authenticate(**credentials):
         if user is None:
             continue
         # Annotate the user object with the path of the backend.
-        user.backend = str(backend.__class__)
+        user.backend = "%s.%s" % (backend.__module__, backend.__class__.__name__)
         return user
 
 def login(request, user):