diff --git a/neutron/plugins/ml2/plugin.py b/neutron/plugins/ml2/plugin.py
index 3edc649ac8f..f0dfd47dc5d 100644
--- a/neutron/plugins/ml2/plugin.py
+++ b/neutron/plugins/ml2/plugin.py
@@ -1097,8 +1097,7 @@ class Ml2Plugin(db_base_plugin_v2.NeutronDbPluginV2,
                 # removed in Queens when we populate all mtu attributes and
                 # enforce it's not nullable on database level
                     db_network.mtu is None):
-                db_network.mtu = self._get_network_mtu(db_network,
-                                                       validate=False)
+                db_network.mtu = self._get_network_mtu(db_network)
                 # agents should now update all ports to reflect new MTU
                 need_network_update_notify = True
 
diff --git a/neutron/tests/fullstack/test_mtu.py b/neutron/tests/fullstack/test_mtu.py
index 87604b3015c..0333e109d5a 100644
--- a/neutron/tests/fullstack/test_mtu.py
+++ b/neutron/tests/fullstack/test_mtu.py
@@ -12,7 +12,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-# from neutronclient.common import exceptions
+from neutronclient.common import exceptions
 from oslo_utils import uuidutils
 
 from neutron.tests.fullstack import base
@@ -44,11 +44,19 @@ class MTUNetworkTestSetup(base.BaseFullStackTestCase):
 
 class TestMTUScenarios(MTUNetworkTestSetup):
 
-    def test_mtu_update_delete_network(self):
+    def test_mtu_update_network_neg(self):
         network = self.safe_client.create_network(self.tenant_id,
                                                   name='mtu-test-network',
                                                   mtu=1450)
-        self.safe_client.update_network(network['id'], mtu=9000)
+        self.assertRaises(exceptions.BadRequest,
+                          self.safe_client.update_network,
+                          network['id'], mtu=9000)
+
+    def test_mtu_update_delete_network(self):
+        network = self.safe_client.create_network(self.tenant_id,
+                                                  name='mtu-test-network',
+                                                  mtu=1200)
+        self.safe_client.update_network(network['id'], mtu=1450)
         res = self.safe_client.delete_network(network['id'])
         self.assertEqual((), res)