diff --git a/nova/tests/fixtures.py b/nova/tests/fixtures.py
index 58ef19e..f72e4e6 100644
--- a/nova/tests/fixtures.py
+++ b/nova/tests/fixtures.py
@@ -584,14 +584,19 @@ class StableObjectJsonFixture(fixtures.Fixture):
     def setUp(self):
         super(StableObjectJsonFixture, self).setUp()

-        def _doit(obj, *args, **kwargs):
+        def _obj_to_prim_sorter(obj, *args, **kwargs):
             result = self._original_otp(obj, *args, **kwargs)
             if 'nova_object.changes' in result:
                 result['nova_object.changes'].sort()
             return result

+        # NOTE(alaski): This makes _obj_to_prim_sorter into an instancemethod
+        # so that its signature matches the method it's patching
+        obj_base.NovaObject._obj_to_prim_sorter = _obj_to_prim_sorter
+
         self.useFixture(fixtures.MonkeyPatch(
-            'nova.objects.base.NovaObject.obj_to_primitive', _doit))
+            'nova.objects.base.NovaObject.obj_to_primitive',
+            obj_base.NovaObject._obj_to_prim_sorter))


 class EngineFacadeFixture(fixtures.Fixture):