Android : Remove if-modified-since header from okhttp request

okhttp sends both if-modified-since date and if-none-match checksum headers to my server. I don't need both and if-none-match is enough to figure out the version the client has. Sending both just confuses my server.

I have tried

builder = new Request.Builder().removeHeader("if-modified-since");

But that doesn't seem to do it. I assume the header is added later.

Is there a way to tell okhttp not to send if-modified-since ?