A duplex printer module includes an elongate housing. The housing defines a print media entry slot at one end, a print media exit slot at the other end, a print media path located between the entry and exit slots, and a plurality of engagement formations with which printer feet can engage. A print engine is mounted within the housing and includes a pair of opposed ink ejecting printhead assemblies between which the print media path passes so that double sided printing of print media passing along the print media path can be effected. Feet extend from the housing and can engage with the engagement formations of another printer to facilitate stacking of the printers together.