A patient interface device (e.g., nasal pillows, a nasal mask or a full-face mask) for delivering breathable gas to a patient has a frame with a main body and a side frame member provided on each lateral side of the main body, each side frame member including a first connector portion, and a headgear assembly removably attachable to the frame, the headgear assembly having a second connector portion adapted to be removably coupled with the first connector portion provided on the frame. The first connector portion and the second connector portion are configured for rotationally locking engagement in a plurality of different rotationally locked positions in which the first and second connector portions may not rotate relative to one another, such that the headgear assembly is rotationally adjustable with respect to the frame.