A system configured for compensating for variations in air density in a pressure support device, the system comprising: a flow generator configured to generate a pressurized flow of breathable gas for delivery to the airway of a subject; at least one sensor configured to provide one or more output signals conveying information relating to one or more parameters associated with an ambient environment of the pressure support device; and one or more processors configured to execute computer program modules, the computer program modules comprising: an ambient parameter determination module configured to determine individual ones of the one or more parameters associated with the ambient environment of the pressure support device based on individual ones of the one or more output signals provided by the at least one sensor; characterized in that the computer program modules further comprise: an ambient air density estimation module configured to estimate an ambient air density of the ambient environment of the pressure support device based on individual ones of the one or more parameters determined by the ambient parameter determination module; an ambient parameter assumption module configured to determine one or more assumed parameters associated with the ambient environment of the pressure support device based on typical sleeping conditions of the subject in case the corresponding parameters cannot be determined by the ambient parameter determination module, wherein the system further comprises a user interface for entering the one or more assumed parameters, and wherein typical sleeping conditions describe normal ambient air temperatures and/or normal ambient air humidities in the environment in which the subject sleeps; and a flow generator control module configured to control the flow generator to adjust a flow rate of the pressurized flow of breathable gas based on the estimated ambient air density of the ambient environment of the pressure support device such that the flow rate of the pressurized flow delivered to the airway of the subject is controlled to compensate for variations in ambient air density. a flow generator configured to generate a pressurized flow of breathable gas for delivery to the airway of a subject; at least one sensor configured to provide one or more output signals conveying information relating to one or more parameters associated with an ambient environment of the pressure support device; and one or more processors configured to execute computer program modules, the computer program modules comprising: an ambient parameter determination module configured to determine individual ones of the one or more parameters associated with the ambient environment of the pressure support device based on individual ones of the one or more output signals provided by the at least one sensor; an ambient air density estimation module configured to estimate an ambient air density of the ambient environment of the pressure support device based on individual ones of the one or more parameters determined by the ambient parameter determination module; an ambient parameter assumption module configured to determine one or more assumed parameters associated with the ambient environment of the pressure support device based on typical sleeping conditions of the subject in case the corresponding parameters cannot be determined by the ambient parameter determination module, wherein the system further comprises a user interface for entering the one or more assumed parameters, and wherein typical sleeping conditions describe normal ambient air temperatures and/or normal ambient air humidities in the environment in which the subject sleeps; and a flow generator control module configured to control the flow generator to adjust a flow rate of the pressurized flow of breathable gas based on the estimated ambient air density of the ambient environment of the pressure support device such that the flow rate of the pressurized flow delivered to the airway of the subject is controlled to compensate for variations in ambient air density.