Theoretical question about Zobrist hashing and chances of collision with slight modification

I’m using zobrist hashing, but for certain positions I want to put them in the cache but make them unique. This is what I’m doing:

quint64 hash = position.zobristHash(); if (makeItUnique)     hash ^= reinterpret_cast<quint64>(this); 

Is there any reason to suppose that what I’m doing will increase the likelihood of hash collisions?