Serving ZIP files using Django

I have generated ZIP files on the fly and served them using Django for a time. Serving ZIP files worked well until it didn’t and browsing StackOverflow etc. didn’t produce clear answers either. The development server worked fine, but gunicorn/nginx didn’t.

In the end, I had to change content_type="application/zip" to content_type="application/x-zip-compressed". I still don’t know what changed and I have only theories why that’s necessary, but maybe it helps someone else. Sometimes it’s better to be dumber about it.