A patient interface comprising: a plenum chamber pressurisable to a therapeutic pressure of at least 6 cmH2O above ambient air pressure, said plenum chamber including a plenum chamber inlet port sized and structured to receive a flow of air at the therapeutic pressure for breathing by a patient; a first seal-forming structure constructed and arranged to form a seal with a region of the patient's face surrounding an entrance to the patient's mouth such that the flow of air at said therapeutic pressure is delivered to the mouth, the first seal-forming structure constructed and arranged to maintain said therapeutic pressure in the plenum chamber throughout the patient's respiratory cycle in use; a second seal-forming structure constructed and arranged to form a seal with a region of the patient's face surrounding an entrance to the patient's nose such that the flow of air at said therapeutic pressure is delivered to the nose, the second seal-forming structure constructed and arranged to maintain said therapeutic pressure in the plenum chamber throughout the patient's respiratory cycle in use; and a vent structure to allow a continuous flow of gases exhaled by the patient from an interior of the plenum chamber to vent to ambient, said vent structure being sized and shaped to maintain the therapeutic pressure in the plenum chamber in use; characterized in that the patent interface further comprises: a pair of support portions disposed within the plenum chamber and provided on opposite sides of the interface, the pair of support portions contact and extend between the second seal forming structure and an anterior wall of the plenum chamber, wherein the pair of support portions are configured to oppose compression in an anterior-posterior direction. a plenum chamber pressurisable to a therapeutic pressure of at least 6 cmH2O above ambient air pressure, said plenum chamber including a plenum chamber inlet port sized and structured to receive a flow of air at the therapeutic pressure for breathing by a patient; a first seal-forming structure constructed and arranged to form a seal with a region of the patient's face surrounding an entrance to the patient's mouth such that the flow of air at said therapeutic pressure is delivered to the mouth, the first seal-forming structure constructed and arranged to maintain said therapeutic pressure in the plenum chamber throughout the patient's respiratory cycle in use; a second seal-forming structure constructed and arranged to form a seal with a region of the patient's face surrounding an entrance to the patient's nose such that the flow of air at said therapeutic pressure is delivered to the nose, the second seal-forming structure constructed and arranged to maintain said therapeutic pressure in the plenum chamber throughout the patient's respiratory cycle in use; and a vent structure to allow a continuous flow of gases exhaled by the patient from an interior of the plenum chamber to vent to ambient, said vent structure being sized and shaped to maintain the therapeutic pressure in the plenum chamber in use; characterized in that the patent interface further comprises: a pair of support portions disposed within the plenum chamber and provided on opposite sides of the interface, the pair of support portions contact and extend between the second seal forming structure and an anterior wall of the plenum chamber, wherein the pair of support portions are configured to oppose compression in an anterior-posterior direction.