diff --git a/nova/api/openstack/placement/handlers/inventory.py b/nova/api/openstack/placement/handlers/inventory.py
index b9f26ebbf..3fed8ac42 100644
--- a/nova/api/openstack/placement/handlers/inventory.py
+++ b/nova/api/openstack/placement/handlers/inventory.py
@@ -362,7 +362,8 @@ def delete_inventories(req):
     except exception.InventoryInUse as ex:
         # NOTE(mriedem): This message cannot change without impacting the
         # nova.scheduler.client.report._RE_INV_IN_USE regex.
-        raise webob.exc.HTTPConflict(ex.format_message())
+        raise webob.exc.HTTPConflict(ex.format_message(),
+                                     comment=errors.INVENTORY_INUSE)
 
     response = req.response
     response.status = 204
diff --git a/nova/tests/functional/api/openstack/placement/gabbits/with-allocations.yaml b/nova/tests/functional/api/openstack/placement/gabbits/with-allocations.yaml
index c1c903a22..03274cadd 100644
--- a/nova/tests/functional/api/openstack/placement/gabbits/with-allocations.yaml
+++ b/nova/tests/functional/api/openstack/placement/gabbits/with-allocations.yaml
@@ -55,6 +55,19 @@ tests:
   response_strings:
       - "Inventory for 'VCPU, DISK_GB' on resource provider '$ENVIRON['RP_UUID']' in use"
 
+- name: fail to delete all inventory 1.23
+  DELETE: /resource_providers/$ENVIRON['RP_UUID']/inventories
+  request_headers:
+      accept: application/json
+      openstack-api-version: placement 1.23
+  status: 409
+  response_headers:
+      content-type: /application/json/
+  response_strings:
+      - "Inventory for 'VCPU, DISK_GB' on resource provider '$ENVIRON['RP_UUID']' in use"
+  response_json_paths:
+      $.errors[0].code: placement.inventory.inuse
+
 - name: get total usages by project
   GET: /usages?project_id=$ENVIRON['PROJECT_ID']
   request_headers: