An injector for gaseous fuel, the injector comprising a body provided with a fuel feed duct and with a fuel delivery duct, the fuel feed duct and the fuel delivery duct opening out into a chamber of the body in which there are mounted a valve member and an actuator means for actuating the valve member between a closed position and an open position in which the valve member defines a fuel flow section, wherein the fuel delivery duct comprises a calibrated segment of section smaller than the flow section defined by the valve member when in the open position.