A Brain Teaser ...

Something a little different today. I like brain teaser's and logic problems ... this is a pretty tough one:

You are a prisoner in a room with only two doors. You know that one of these doors leads to your freedom while the other door leads to a room filled with hungry lions. Guarding each door is a single guard (one at each of the two doors). You know that one of these guards has been instructed to lie no matter what while the other guard has been instructed to tell the truth no matter what. Unfortunately, you do not know which door or which guard is which!

You are allowed to ask one question to one of the guards in order to discern which door to take to safety. What do you do?