A pagewidth printhead is provided for an inkjet printer. The printhead includes an elongate support. A plurality of printhead modules is supported by the support. Each printhead module includes rows of unit cells. Each unit cell includes a nozzle through which ink can be ejected and an actuator configured to eject ink from the nozzle. Opposite edges of each printhead module define complementary formations so that the printhead modules can be engaged together in series along the support.