A fluid adapter for a breathable gas delivery device for delivering breathable gas to a user, the fluid adapter comprising: an adapter body defining an adapter chamber with at least one fluid passageway extending through the adapter body into the adapter chamber; an ambient air inlet port arranged to provide fluid communication between the adapter chamber and ambient air outside of the fluid adapter; an adapter outlet port in fluid communication with the adapter chamber and arranged to be fluidically coupled to a delivery device gas inlet port of the breathable gas delivery device; an adapter connector arranged to connect the fluid adapter to the breathable gas delivery device such that the adapter outlet port is fluidically coupled to the delivery device gas inlet port; a rotatable part comprising an annular member and a pressurised gas inlet port arranged to be fluidically coupled to a source of pressurised breathable gas, the rotatable part being rotatably coupled to the adapter body with the annular member surrounding the adapter body such that the rotatable part can be rotated to a plurality of angular positions with respect to the adapter body so as to alter the position of the pressurised gas inlet port, wherein in each of the angular positions the pressurised gas inlet port is in fluid communication with the adapter chamber through the at least one fluid passageway; characterized by an annular fluid channel between the adapter body and the annular member into which the pressurised gas inlet port and the at least one fluid passageway opens so as to ensure fluid communication between the pressurised gas inlet port and the adapter chamber regardless of the angular position of the rotatable part. an adapter body defining an adapter chamber with at least one fluid passageway extending through the adapter body into the adapter chamber; an ambient air inlet port arranged to provide fluid communication between the adapter chamber and ambient air outside of the fluid adapter; an adapter outlet port in fluid communication with the adapter chamber and arranged to be fluidically coupled to a delivery device gas inlet port of the breathable gas delivery device; an adapter connector arranged to connect the fluid adapter to the breathable gas delivery device such that the adapter outlet port is fluidically coupled to the delivery device gas inlet port; a rotatable part comprising an annular member and a pressurised gas inlet port arranged to be fluidically coupled to a source of pressurised breathable gas, the rotatable part being rotatably coupled to the adapter body with the annular member surrounding the adapter body such that the rotatable part can be rotated to a plurality of angular positions with respect to the adapter body so as to alter the position of the pressurised gas inlet port, wherein in each of the angular positions the pressurised gas inlet port is in fluid communication with the adapter chamber through the at least one fluid passageway; characterized by an annular fluid channel between the adapter body and the annular member into which the pressurised gas inlet port and the at least one fluid passageway opens so as to ensure fluid communication between the pressurised gas inlet port and the adapter chamber regardless of the angular position of the rotatable part.