How to use reqirep with https requests?

I’m using the following instruction which works just fine for http requests:

reqirep ^([^\ :]*)\ /.*([a-z][a-z]-[a-z][a-z]).pdf     \1\ /\2/404 if needsredirect !ischina

But for https requests this generates a HTTP/1.1 400 Bad Request and I can’t figure out how to get this to work. Any help much appreciated.