A modular printhead assembly is provided for an inkjet printer. The modular printhead assembly includes an elongate chassis defining a plurality of slots. An elongate ink reservoir is fast with the chassis. The ink reservoir defines: a plurality of longitudinally extending ink channels for storing respective types of ink, a plurality of spaced apart sets of ink outlets with the ink outlets of each set being in fluid communication with respective ink channels, and a plurality of receiving formations located along the ink reservoir which can receive a plurality of printhead modules. The plurality of printhead modules is configured to releasably engage with respective sets of ink outlets and print ink supplied from the ink reservoir. Each printhead module includes a plurality of resilient fastening legs configured to be received within the receiving formations at particular locations during engagement so that access to the legs is thereafter enabled through the slots to facilitate disengagement of the printhead modules from the ink reservoir.