This invention relates to a cover assembly for a cradle unit of a pagewidth print engine. The cover assembly defines a docking port for a refill unit configured to refill a cartridge unit of the print engine. The cartridge unit is housed in the cradle. The docking port includes a rim portion, engagement means and a push rod. The rim portion is for receiving a base portion of the refill unit so that the refill unit is able to pass through the cover assembly, in use, to dock with the cartridge unit. The engagement means is located within the rim portion, the engagement means being configured to engage the refill unit to retain the refill unit securely in position to facilitate refilling of the cartridge unit. The push rod extends through a hole in the rim portion for operatively actuating the refill unit to incrementally dispense ink.