Continuous Loop Playback?

This one has me baffled. I'm trying to set a selection on the timeline and have that section do a continous loop playback. So I select a section on the timeline. Then I click on the "Set loop points to selection", then I set the Loop On/off to ON. So it plays back the selected loop section once and then stops at the beginning of the loop. How do I have it continue to do a playback loop of that section?