Look under and inside, there should be a set screw. Don't ride it like that, it would put increased strain on the hinge which would break off.
Aaah, thank you. Yes, there's only a screw on the one side of it, it's missing on the other end. I'll have to head to Home Depot or something to see if I can find a replacement for the other side. You wouldn't happen to know the dimensions of the screw, would you? Otherwise I'll just bring the one I have with me and try to duplicate it.