diff --git a/nova/test.py b/nova/test.py
index ea8c13505f10..2e3012ffcd51 100644
--- a/nova/test.py
+++ b/nova/test.py
@@ -226,6 +226,8 @@ class TestCase(testtools.TestCase):
             objects_base.NovaObjectRegistry._registry._obj_classes)
         self.addCleanup(self._restore_obj_registry)
 
+        self.useFixture(nova_fixtures.StableObjectJsonFixture())
+
         # NOTE(mnaser): All calls to utils.is_neutron() are cached in
         # nova.utils._IS_NEUTRON.  We set it to None to avoid any
         # caching of that value.
diff --git a/nova/tests/fixtures.py b/nova/tests/fixtures.py
index 39467cccca32..2607eae11f13 100644
--- a/nova/tests/fixtures.py
+++ b/nova/tests/fixtures.py
@@ -446,3 +446,31 @@ class BannedDBSchemaOperations(fixtures.Fixture):
             self.useFixture(fixtures.MonkeyPatch(
                 'sqlalchemy.%s.alter' % thing,
                 lambda *a, **k: self._explode(thing, 'alter')))
+
+
+class StableObjectJsonFixture(fixtures.Fixture):
+    """Fixture that makes sure we get stable JSON object representations.
+
+    Since objects contain things like set(), which can't be converted to
+    JSON, we have some situations where the representation isn't fully
+    deterministic. This doesn't matter at all at runtime, but does to
+    unit tests that try to assert things at a low level.
+
+    This fixture mocks the obj_to_primitive() call and makes sure to
+    sort the list of changed fields (which came from a set) before
+    returning it to the caller.
+    """
+    def __init__(self):
+        self._original_otp = obj_base.NovaObject.obj_to_primitive
+
+    def setUp(self):
+        super(StableObjectJsonFixture, self).setUp()
+
+        def _doit(obj, *args, **kwargs):
+            result = self._original_otp(obj, *args, **kwargs)
+            if 'nova_object.changes' in result:
+                result['nova_object.changes'].sort()
+            return result
+
+        self.useFixture(fixtures.MonkeyPatch(
+            'nova.objects.base.NovaObject.obj_to_primitive', _doit))
diff --git a/nova/tests/unit/test_fixtures.py b/nova/tests/unit/test_fixtures.py
index 16b87cea4795..f0764fada563 100644
--- a/nova/tests/unit/test_fixtures.py
+++ b/nova/tests/unit/test_fixtures.py
@@ -331,3 +331,17 @@ class TestBannedDBSchemaOperations(testtools.TestCase):
                               table.drop)
             self.assertRaises(exception.DBNotAllowed,
                               table.alter)
+
+
+class TestStableObjectJsonFixture(testtools.TestCase):
+    def test_changes_sort(self):
+        class TestObject(obj_base.NovaObject):
+            def obj_what_changed(self):
+                return ['z', 'a']
+
+        obj = TestObject()
+        self.assertEqual(['z', 'a'],
+                         obj.obj_to_primitive()['nova_object.changes'])
+        with fixtures.StableObjectJsonFixture():
+            self.assertEqual(['a', 'z'],
+                             obj.obj_to_primitive()['nova_object.changes'])