Continuos Vapor Barrier

I'm redoing the bathroom shower which runs along an exterior wall. It originally had drywall in the wet area and I'm changing that to cement board.
When I cut out the drywall along a corner wall, I also cut through the 2 mil polyethylene vapour barrier that was there, so I am not able to join the seams of the new 6 mil that I'm installing to the original where it passes behind this side wall.

What are my options here?