Incoming redirect from Ghost strips .html from end of URL

I have an incoming URL redirected from my Ghost site.

The redirect in my Ghost redirects.yaml file is:

/murder-your-darlings: Murder your darlings

Somewhere between Ghost and the html suffix is stripped, so the redirect goes my 404 page.

I suspect (but don’t know) the problem lies with the way Ghost interprets redirects.yaml.

Is there anything I can do at the end to fix this or is it all down to Ghost?