Using third party dll with a #def CPP

Hey all, I am moving a suite of plugins from 4.13 to 4.15, and am pulling my hair out.

I have a third party dll / lib that is integrated in my plugin, and it has a ::CPP namespace.

UE has the same, and so I get aaalll kinds of compile errors. I have:

#pragma once
#define PCPP CPP
#undef CPP

at the top of my header, but It makes no difference. What else can i do to get building?

Thanks!