diff --git a/django/contrib/auth/models.py b/django/contrib/auth/models.py
index 042420aa8a..090b6d40c8 100644
--- a/django/contrib/auth/models.py
+++ b/django/contrib/auth/models.py
@@ -404,6 +404,7 @@ class User(models.Model):
 
 class AnonymousUser(object):
     id = None
+    pk = None
     username = ''
     is_staff = False
     is_active = False
diff --git a/django/contrib/auth/tests/basic.py b/django/contrib/auth/tests/basic.py
index 512de163d9..4c2e8cd8aa 100644
--- a/django/contrib/auth/tests/basic.py
+++ b/django/contrib/auth/tests/basic.py
@@ -52,6 +52,7 @@ class BasicTestCase(TestCase):
     def test_anonymous_user(self):
         "Check the properties of the anonymous user"
         a = AnonymousUser()
+        self.assertEqual(a.pk, None)
         self.assertFalse(a.is_authenticated())
         self.assertFalse(a.is_staff)
         self.assertFalse(a.is_active)