Only one key handled per tick?

I'm working through _Hands On Rust_ and one thing I've noticed is that the game feels a little laggy. I think this is because it is sometimes dropping keypresses, e.g. if I press "up" followed quickly by "down", sometimes the "down" event isn't processed. I think this is due to the fact that the keyboard is only checked once per tick.

Is there some way to guarantee that the game processes every keyboard event that happens?