diff --git a/heat/engine/resource.py b/heat/engine/resource.py
index 3da6f2d55d..147f835e01 100644
--- a/heat/engine/resource.py
+++ b/heat/engine/resource.py
@@ -243,7 +243,7 @@ class Resource(status.ResourceStatus):
         self.updated_time = stack.updated_time
         self._rpc_client = None
         self.needed_by = []
-        self.requires = []
+        self.requires = set()
         self.replaces = None
         self.replaced_by = None
         self.current_template_id = None
@@ -291,7 +291,7 @@ class Resource(status.ResourceStatus):
         self.created_time = resource.created_at
         self.updated_time = resource.updated_at
         self.needed_by = resource.needed_by
-        self.requires = resource.requires
+        self.requires = set(resource.requires)
         self.replaces = resource.replaces
         self.replaced_by = resource.replaced_by
         self.current_template_id = resource.current_template_id
@@ -392,7 +392,7 @@ class Resource(status.ResourceStatus):
               'name': self.name,
               'rsrc_prop_data_id': None,
               'needed_by': self.needed_by,
-              'requires': list(requires),
+              'requires': sorted(requires, reverse=True),
               'replaces': self.id,
               'action': self.INIT,
               'status': self.COMPLETE,
@@ -1158,7 +1158,7 @@ class Resource(status.ResourceStatus):
                            timeout, progress_callback=None):
         """Creates the resource by invoking the scheduler TaskRunner."""
         self._calling_engine_id = engine_id
-        self.requires = list(requires)
+        self.requires = requires
         self.current_template_id = template_id
         if self.stack.adopt_stack_data is None:
             runner = scheduler.TaskRunner(self.create)
@@ -1648,7 +1648,7 @@ class Resource(status.ResourceStatus):
         self.updated_time = datetime.utcnow()
 
         if new_requires is not None:
-            self.requires = list(set(self.requires) | new_requires)
+            self.requires = self.requires | new_requires
 
         with self._action_recorder(action, UpdateReplace):
             after_props.validate()
@@ -1678,7 +1678,7 @@ class Resource(status.ResourceStatus):
             self.reparse()
             self._update_stored_properties()
             if new_requires is not None:
-                self.requires = list(new_requires)
+                self.requires = new_requires
 
         yield self._break_if_required(
             self.UPDATE, environment.HOOK_POST_UPDATE)
@@ -2071,7 +2071,7 @@ class Resource(status.ResourceStatus):
               'rsrc_prop_data_id':
                   self._create_or_replace_rsrc_prop_data(),
               'needed_by': self.needed_by,
-              'requires': self.requires,
+              'requires': sorted(self.requires, reverse=True),
               'replaces': self.replaces,
               'replaced_by': self.replaced_by,
               'current_template_id': self.current_template_id,
diff --git a/heat/tests/test_convg_stack.py b/heat/tests/test_convg_stack.py
index 191a7b3e87..0d1bc26a37 100644
--- a/heat/tests/test_convg_stack.py
+++ b/heat/tests/test_convg_stack.py
@@ -800,7 +800,7 @@ class TestConvgComputeDependencies(common.HeatTestCase):
         res = mock.MagicMock()
         res.id = 6
         res.name = 'E'
-        res.requires = [3]
+        res.requires = {3}
         res.replaces = 1
         res.current_template_id = 2
         db_resources[6] = res
diff --git a/heat/tests/test_resource.py b/heat/tests/test_resource.py
index e1effa0ce1..9ed14bfc1f 100644
--- a/heat/tests/test_resource.py
+++ b/heat/tests/test_resource.py
@@ -720,7 +720,7 @@ class ResourceTest(common.HeatTestCase):
         self.assertEqual(res.id, new_res.replaces)
         self.assertIsNone(new_res.physical_resource_id)
         self.assertEqual(new_tmpl_id, new_res.current_template_id)
-        self.assertItemsEqual(list(new_requires), new_res.requires)
+        self.assertEqual([4, 2, 1], new_res.requires)
 
     def test_metadata_default(self):
         tmpl = rsrc_defn.ResourceDefinition('test_resource', 'Foo')
@@ -2131,7 +2131,7 @@ class ResourceTest(common.HeatTestCase):
         stack.thread_group_mgr = tools.DummyThreadGroupManager()
         stack.converge_stack(stack.t, action=stack.CREATE)
         res = stack.resources['test_res']
-        res.requires = [2]
+        res.requires = {2}
         res.action = res.CREATE
         res.store()
         self._assert_resource_lock(res.id, None, None)
@@ -2231,7 +2231,7 @@ class ResourceTest(common.HeatTestCase):
     def test_update_in_progress_convergence(self, mock_cfcr, mock_nu):
         tmpl = rsrc_defn.ResourceDefinition('test_res', 'Foo')
         res = generic_rsrc.GenericResource('test_res', tmpl, self.stack)
-        res.requires = [1, 2]
+        res.requires = {1, 2}
         res.store()
         rs = resource_objects.Resource.get_obj(self.stack.context, res.id)
         rs.update_and_save({'engine_id': 'not-this'})
@@ -2255,7 +2255,7 @@ class ResourceTest(common.HeatTestCase):
         self.assertEqual(msg, six.text_type(ex))
         # ensure requirements are not updated for failed resource
         rs = resource_objects.Resource.get_obj(self.stack.context, res.id)
-        self.assertEqual([1, 2], rs.requires)
+        self.assertEqual([2, 1], rs.requires)
 
     @mock.patch.object(resource.Resource, 'update_template_diff_properties')
     @mock.patch.object(resource.Resource, '_needs_update')
@@ -2272,7 +2272,7 @@ class ResourceTest(common.HeatTestCase):
         stack.thread_group_mgr = tools.DummyThreadGroupManager()
         stack.converge_stack(stack.t, action=stack.CREATE)
         res = stack.resources['test_res']
-        res.requires = [2]
+        res.requires = {2}
         res.store()
         self._assert_resource_lock(res.id, None, None)
 
@@ -2313,7 +2313,7 @@ class ResourceTest(common.HeatTestCase):
         stack.thread_group_mgr = tools.DummyThreadGroupManager()
         stack.converge_stack(stack.t, action=stack.CREATE)
         res = stack.resources['test_res']
-        res.requires = [2]
+        res.requires = {2}
         res.store()
         self._assert_resource_lock(res.id, None, None)