Absolutely dude. In fact you should ask for more. This is not only good for you but it benefits them as well. If you have a vested interest in the company succeeding, you'll naturally be more devoted to it.

The bottom line is, regardless of what people may say, working at a startup is risky and you will more than likely end up working more than your cubical-dwelling counterparts. Ownership is what makes this okay at the end of the day.