diff --git a/rest_framework/mixins.py b/rest_framework/mixins.py
index 1edcfa5c9..a49d7a2f2 100644
--- a/rest_framework/mixins.py
+++ b/rest_framework/mixins.py
@@ -106,6 +106,10 @@ class UpdateModelMixin(object):
         # pk and/or slug attributes are implicit in the URL.
         pk = self.kwargs.get(self.pk_url_kwarg, None)
         if pk:
+            try:
+                pk = int(pk)
+            except ValueError:
+                pass
             setattr(obj, 'pk', pk)
 
         slug = self.kwargs.get(self.slug_url_kwarg, None)
diff --git a/rest_framework/tests/generics.py b/rest_framework/tests/generics.py
index 14fa66f93..7c24d84ea 100644
--- a/rest_framework/tests/generics.py
+++ b/rest_framework/tests/generics.py
@@ -175,7 +175,7 @@ class TestInstanceView(TestCase):
         content = {'text': 'foobar'}
         request = factory.put('/1', json.dumps(content),
                               content_type='application/json')
-        response = self.view(request, pk=1).render()
+        response = self.view(request, pk='1').render()
         self.assertEquals(response.status_code, status.HTTP_200_OK)
         self.assertEquals(response.data, {'id': 1, 'text': 'foobar'})
         updated = self.objects.get(id=1)