A structure for an inkjet printhead is disclosed. The printhead structure has an elongate support structure for supporting a printhead integrated circuit, and ink conduits formed in the elongate support structure for supplying ink to an array of nozzles of the printhead integrated circuit. Each ink conduit includes cavities distributed along a roof of the ink conduit. An opening to each cavity has an upstream edge and a downstream edge. The upstream edge contacts the ink before the downstream edge during initial priming of the ink conduits from an ink supply. The upstream edge has a transition face between the ink conduit and the cavity interior, the transition face being configured to inhibit ink from filling the cavity by capillary action during initial priming of the ink conduit. This causes gas to be trapped within the cavity. The gas acts to compress pressure pulses in the ink.