diff --git a/rest_framework/tests/serializer.py b/rest_framework/tests/serializer.py
index 00fb689af..7d750b813 100644
--- a/rest_framework/tests/serializer.py
+++ b/rest_framework/tests/serializer.py
@@ -340,7 +340,11 @@ class ManyToManyTests(TestCase):
         """
         data = {}
         serializer = self.serializer_class(data=data)
-        self.assertEqual(serializer.is_valid(), False)
+        self.assertEqual(serializer.is_valid(), True)
+        instance = serializer.save()
+        self.assertEquals(len(ManyToManyModel.objects.all()), 3)
+        self.assertEquals(instance.pk, 3)
+        self.assertEquals(list(instance.rel.all()), [])
 
 
     def test_create_empty_relationship_flat_data(self):