That is Popper’s own proposed solution for that paradox: Tolerance is not to be extended to the intolerant.

He suggests trying to work within the bounds of the contract first (talking, reasoning, voting etc.), but if that fails or is impossible endorses the censorship and suppression (violent, if necessary) of the intolerant. Try the high road, but be willing to acknowledge when that road is a dead end and ready to correct course in time.