I can't put a strap on my acoustic guitar, what's with it?

Every guitar has two nuts/knobs/things to hook a strap onto, right? Well, for some reason my acoustic guitar only has one. My parents got it for me from a pawn shop as a gift, so I can't really talk to the people that last had it or anything. Are some guitars just built this way for some reason? And is it possible for me to get another nut installed so I can put a strap on this thing? (If so, do you have any idea how much that might cost?)