foo.diff

diff --git a/django/contrib/auth/models.py b/django/contrib/auth/models.py
index 5b89fe8..e8c796a 100644
--- a/django/contrib/auth/models.py
+++ b/django/contrib/auth/models.py
@@ -13,7 +13,6 @@ from django.contrib import auth
 from django.contrib.auth.hashers import (
     check_password, make_password, is_password_usable)
 from django.contrib.auth.signals import user_logged_in
-from django.contrib.contenttypes.models import ContentType
 from django.utils.encoding import python_2_unicode_compatible
 
 
@@ -29,6 +28,10 @@ user_logged_in.connect(update_last_login)
 
 class PermissionManager(models.Manager):
     def get_by_natural_key(self, codename, app_label, model):
+        # Import here since the contenttypes app may not be ready
+        # when this file is imported.
+        from django.contrib.contenttypes.models import ContentType
+
         return self.get(
             codename=codename,
             content_type=ContentType.objects.get_by_natural_key(app_label,
@@ -61,7 +64,7 @@ class Permission(models.Model):
     created for each Django model.
     """
     name = models.CharField(_('name'), max_length=50)
-    content_type = models.ForeignKey(ContentType)
+    content_type = models.ForeignKey('contenttypes.ContentType')
     codename = models.CharField(_('codename'), max_length=100)
     objects = PermissionManager()