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; wherein the patient interface further comprises: a boundary between the first seal-forming structure and the second seal-forming structure comprising a ridge, and a pair of support portions provided on opposite sides of the interface between the second seal forming structure and an anterior wall of the plenum chamber, the support portions being configured to oppose compression in the anterior-posterior direction, wherein the ridge and support portions are configured to reduce creasing on or adjacent the ridge, and wherein the support portions are provided to portions of the second seal forming structure which seal, in use, against the patient's lip superior. 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; wherein the patient interface further comprises: a boundary between the first seal-forming structure and the second seal-forming structure comprising a ridge, and a pair of support portions provided on opposite sides of the interface between the second seal forming structure and an anterior wall of the plenum chamber, the support portions being configured to oppose compression in the anterior-posterior direction, a boundary between the first seal-forming structure and the second seal-forming structure comprising a ridge, and a pair of support portions provided on opposite sides of the interface between the second seal forming structure and an anterior wall of the plenum chamber, the support portions being configured to oppose compression in the anterior-posterior direction, wherein the ridge and support portions are configured to reduce creasing on or adjacent the ridge, and wherein the support portions are provided to portions of the second seal forming structure which seal, in use, against the patient's lip superior.