diff --git a/neutron/db/l3_db.py b/neutron/db/l3_db.py
index 85751a0cf0..a8a0613fc2 100644
--- a/neutron/db/l3_db.py
+++ b/neutron/db/l3_db.py
@@ -413,11 +413,11 @@ class L3_NAT_db_mixin(l3.RouterPluginBase):
         return DEVICE_OWNER_ROUTER_INTF
 
     def _validate_interface_info(self, interface_info):
-        if not interface_info:
+        port_id_specified = interface_info and 'port_id' in interface_info
+        subnet_id_specified = interface_info and 'subnet_id' in interface_info
+        if not (port_id_specified or subnet_id_specified):
             msg = _("Either subnet_id or port_id must be specified")
             raise n_exc.BadRequest(resource='router', msg=msg)
-        port_id_specified = 'port_id' in interface_info
-        subnet_id_specified = 'subnet_id' in interface_info
         if port_id_specified and subnet_id_specified:
             msg = _("Cannot specify both subnet-id and port-id")
             raise n_exc.BadRequest(resource='router', msg=msg)
diff --git a/neutron/tests/unit/test_l3_plugin.py b/neutron/tests/unit/test_l3_plugin.py
index 5ecb53f7ba..ccce434800 100644
--- a/neutron/tests/unit/test_l3_plugin.py
+++ b/neutron/tests/unit/test_l3_plugin.py
@@ -789,6 +789,13 @@ class L3NatTestCaseBase(L3NatTestCaseMixin):
                                               None,
                                               p['port']['id'])
 
+    def test_router_add_interface_empty_port_and_subnet_ids(self):
+        with self.router() as r:
+            self._router_interface_action('add', r['router']['id'],
+                                          None, None,
+                                          expected_code=exc.
+                                          HTTPBadRequest.code)
+
     def test_router_add_interface_port_bad_tenant_returns_404(self):
         with mock.patch('neutron.context.Context.to_dict') as tdict:
             admin_context = {'roles': ['admin']}