Titles of advisors on CV (a stupidly minor question)

For my masters thesis, my primary advisor was a professor, and my co-advisor was a post-doc who has since become a professor. When listing my advisors on my CV, should I list it as "Prof. X and Dr. Y", or "Prof. X and Prof. Y"?

It's a silly minor thing, but I'm curious what the "proper" way to do these titles is.