Docs - product feedback: Allow Kroki in the same server

I had run a self-host Docker version GitLab CE server(13.8.0), and I want to use self-host Kroki Docker for visualization. (https://docs.gitlab.com/ee/administration/integration/kroki.html#kroki-server)

There is no problem to run both Gitlab and Kroki Docker on the same server.

But GitLab settings page not allow user to set Kroki URL with the same host with different port. (In Admin Area, Settings, General, Kroki)

The error message:

The form contains the following error:
Kroki url is not valid. Requests to localhost are not allowed

Is it possible to allow user set Kroki URL with the same host?

Thank you.