A pagewidth inkjet printer is described which includes printhead (11) with a plurality of print nozzles (30) for ejecting ink drops towards a print medium. A space is defined between the nozzles and a nozzle guard (43) with a series of apertures (44) aligned with the nozzles. During printing operation, positive air pressure is supplied to this space, the air exiting the space through the apertures, preventing blockage by paper dust. When not printing, the air supply is closed off by air valve member (66) and a capping member (80) on a rotary platen (14) contacts the printhead to maintain a closed atmosphere at the surface of the nozzles, reducing drying of ink on the nozzles.