An elbow assembly for a mask system includes an elbow including a slot and a port, an anti-asphyxia valve adapted to be received within the slot and including a flap portion adapted to selectively close the port depending on the presence of pressurized gas, and a support member to secure the anti-asphyxia valve to the elbow. The support member includes a slot that is adapted to interlock with a protrusion provided to the anti-asphyxia valve.