diff --git a/neutron/objects/base.py b/neutron/objects/base.py
index a0f0c5974a7..8ecca260a29 100644
--- a/neutron/objects/base.py
+++ b/neutron/objects/base.py
@@ -27,6 +27,7 @@ from oslo_versionedobjects import base as obj_base
 from oslo_versionedobjects import exception as obj_exception
 from oslo_versionedobjects import fields as obj_fields
 import six
+from sqlalchemy import orm
 
 from neutron._i18n import _
 from neutron.db import api as db_api
@@ -496,6 +497,10 @@ class NeutronDbObject(NeutronObject):
         for field, field_db in cls.fields_need_translation.items():
             if field_db in result:
                 result[field] = result.pop(field_db)
+        for k, v in result.items():
+            # don't allow sqlalchemy lists to propagate outside
+            if isinstance(v, orm.collections.InstrumentedList):
+                result[k] = list(v)
         return result
 
     @classmethod
diff --git a/neutron/objects/ports.py b/neutron/objects/ports.py
index 3fa59cd5347..40ef7113491 100644
--- a/neutron/objects/ports.py
+++ b/neutron/objects/ports.py
@@ -395,22 +395,31 @@ class Port(base.NeutronDbObject):
         return super(Port, cls).get_objects(context, _pager, validate_filters,
                                             **kwargs)
 
-    # TODO(rossella_s): get rid of it once we switch the db model to using
-    # custom types.
     @classmethod
     def modify_fields_to_db(cls, fields):
         result = super(Port, cls).modify_fields_to_db(fields)
+
+        # TODO(rossella_s): get rid of it once we switch the db model to using
+        # custom types.
         if 'mac_address' in result:
             result['mac_address'] = cls.filter_to_str(result['mac_address'])
+
+        # convert None to []
+        if 'distributed_port_binding' in result:
+            result['distributed_port_binding'] = (
+                result['distributed_port_binding'] or []
+            )
         return result
 
-    # TODO(rossella_s): get rid of it once we switch the db model to using
-    # custom types.
     @classmethod
     def modify_fields_from_db(cls, db_obj):
         fields = super(Port, cls).modify_fields_from_db(db_obj)
+
+        # TODO(rossella_s): get rid of it once we switch the db model to using
+        # custom types.
         if 'mac_address' in fields:
             fields['mac_address'] = utils.AuthenticEUI(fields['mac_address'])
+
         distributed_port_binding = fields.get('distributed_binding')
         if distributed_port_binding:
             fields['distributed_binding'] = fields['distributed_binding'][0]
diff --git a/neutron/tests/unit/objects/test_base.py b/neutron/tests/unit/objects/test_base.py
index 2b6c11bb7b6..a538deebe2a 100644
--- a/neutron/tests/unit/objects/test_base.py
+++ b/neutron/tests/unit/objects/test_base.py
@@ -1977,12 +1977,16 @@ class BaseDbObjectTestCase(_BaseObjectTestCase,
 
         fields_to_update = self.get_updatable_fields(self.obj_fields[1])
         if fields_to_update:
-            old_model = copy.deepcopy(obj.db_obj)
+            old_fields = {}
             for key, val in fields_to_update.items():
+                db_model_attr = (
+                    obj.fields_need_translation.get(key, key))
+                old_fields[db_model_attr] = obj.db_obj[db_model_attr]
                 setattr(obj, key, val)
             obj.update()
             self.assertIsNotNone(obj.db_obj)
-            self.assertNotEqual(old_model, obj.db_obj)
+            for k, v in obj.modify_fields_to_db(fields_to_update).items():
+                self.assertEqual(v, obj.db_obj[k], '%s attribute differs' % k)
 
         obj.delete()
         self.assertIsNone(obj.db_obj)