2 Doors

You approach two doors guarded by two gatekeepers. You know that one door leads to the exit, and the other leads into a never-ending maze, but you don't know which is which. You also know that one of the gatekeepers always tells the truth, and the other always lies, but you don't know which is which. You get one question to ask one of the gatekeepers to figure out which door leads to the exit. What do you ask?