diff --git a/nova/api/openstack/compute/volumes.py b/nova/api/openstack/compute/volumes.py
index 27b9af950293..faa2238e5e7d 100644
--- a/nova/api/openstack/compute/volumes.py
+++ b/nova/api/openstack/compute/volumes.py
@@ -433,7 +433,7 @@ class VolumeAttachmentController(wsgi.Controller):
 
         if bdm.is_root:
             msg = _("Cannot detach a root device volume")
-            raise exc.HTTPForbidden(explanation=msg)
+            raise exc.HTTPBadRequest(explanation=msg)
 
         try:
             self.compute_api.detach_volume(context, instance, volume)
diff --git a/nova/tests/unit/api/openstack/compute/test_volumes.py b/nova/tests/unit/api/openstack/compute/test_volumes.py
index ef47287a25a4..162d472034a5 100644
--- a/nova/tests/unit/api/openstack/compute/test_volumes.py
+++ b/nova/tests/unit/api/openstack/compute/test_volumes.py
@@ -541,7 +541,7 @@ class VolumeAttachTestsV21(test.NoDBTestCase):
                  new_callable=mock.PropertyMock)
     def test_detach_vol_root(self, mock_isroot):
         mock_isroot.return_value = True
-        self.assertRaises(exc.HTTPForbidden,
+        self.assertRaises(exc.HTTPBadRequest,
                           self.attachments.delete,
                           self.req,
                           FAKE_UUID,