How do I keep from biting while giving a BJ?

I have a small mouth an he's rather large an I always end up accidentally biting him,I try to wrap my lips to where they cover my teeth but I still end up biting or my mouth starts hurting an I have to stop or both, it makes me feel bad when I do an so I've got to where I no longer want to give one, I know he likes it an enjoys it at least until I accidentally bite him.