Apparatus to permit a delivery of a flow of breathable gas to a patient's airways. In one version, a coupler extension may include a seat portion to permit use of a mask with a nasal cannula. In some versions, the coupler extension is configured to conduct the flow of gas to prongs of a nasal cannula. The seat portion can receive and seal with a cushion of a respiratory mask and may have a sealing bevel to promote sealing between the cushion of the respiratory mask and a facial contact surface of a user. In some versions, a conduit adapted to communicate a flow of gas may comprise a slit valve formed by a portion of the wall material of the conduit. In some versions, a nasal interface may include naris pillows to seal with and conduct a flow of breathable gas into a nares of a user. Each naris pillow may include a nasal projection to conduct a further flow of gas. The nasal projection may extend within the naris beyond the seal of the naris pillow.