A forehead support for a mask assembly includes a frame connector provided to a mask frame, a forehead cushion support movably mounted to the frame connector for generally linear movement between retracted and extended positions with respect to the frame connector, and an adjustment knob movably mounted to the frame connector and threadably engaged with the forehead cushion support such that turning movement of the adjustment knob causes the forehead cushion support to be moved between the retracted and extended positions. The adjustment knob includes a resilient prong having a ratchet bump. The ratchet bump is adapted to selectively engage a series of ridges provided to the frame connector to provide indexed incremental adjustment.