It sounds like you just did.

I don't know the depth of discussion you've had with the man, but it would seem to me saying something like, "I like to be thrown onto the bed, but into walls is too much," is pretty clear cut? If he understands this in theory, but just gets a little too carried away during play, a lot of couples have success with a safe words. One word can mean "slow down," while another means "stop completely."