A fuel injector for an internal combustion piston engine comprising - an injector body provided with a fuel space in the body, - a fuel inlet for admission of pressurized fuel into the fuel space, - at least one nozzle orifice through which fuel may be injected into a cylinder of the engine, - an injector needle arrangement, a first end of which is arranged in co-operation with the nozzle orifice for opening or closing the orifice, - a spring element forcing the injector needle arrangement towards a position closing the nozzle orifice, and - a piezoelectric actuator arranged to control the position of the injector needle arrangement so as to control opening of a flow communication from the fuel space through the at least one nozzle orifice by retraction movement, - the piezoelectric actuator is in direct connection with a control piston at a first end of the control piston, a second end of which control piston is arranged to extend into a cylinder space arranged into the injector body, and the second end of control piston having a first cross sectional area, - a second end of the injector needle arrangement is arranged to extend from the fuel space into the cylinder space towards the control piston, the second end of the injector needle arrangement having a second cross sectional area, being smaller than the first cross sectional area of the control piston, - the injector body is provided with a fuel discharge duct which opens into the cylinder space, and characterized in that - the cylinder space is arranged in flow connection with the fuel space via a gap between the second end of the injector needle arrangement extending into the cylinder space and the injector body so that the cylinder space is filled with the fuel, and - that the fuel space is continuously in flow communication with the discharge duct for discharging fuel from the fuel space via a flow path successively comprising the gap between the second end of the injector needle arrangement and the injector body, the cylinder space, a gap between the second end of control piston and the injector body, and the discharge duct. - an injector body provided with a fuel space in the body, - a fuel inlet for admission of pressurized fuel into the fuel space, - at least one nozzle orifice through which fuel may be injected into a cylinder of the engine, - an injector needle arrangement, a first end of which is arranged in co-operation with the nozzle orifice for opening or closing the orifice, - a spring element forcing the injector needle arrangement towards a position closing the nozzle orifice, and - a piezoelectric actuator arranged to control the position of the injector needle arrangement so as to control opening of a flow communication from the fuel space through the at least one nozzle orifice by retraction movement, - the piezoelectric actuator is in direct connection with a control piston at a first end of the control piston, a second end of which control piston is arranged to extend into a cylinder space arranged into the injector body, and the second end of control piston having a first cross sectional area, - a second end of the injector needle arrangement is arranged to extend from the fuel space into the cylinder space towards the control piston, the second end of the injector needle arrangement having a second cross sectional area, being smaller than the first cross sectional area of the control piston, - the injector body is provided with a fuel discharge duct which opens into the cylinder space, and characterized in that - the cylinder space is arranged in flow connection with the fuel space via a gap between the second end of the injector needle arrangement extending into the cylinder space and the injector body so that the cylinder space is filled with the fuel, and - that the fuel space is continuously in flow communication with the discharge duct for discharging fuel from the fuel space via a flow path successively comprising the gap between the second end of the injector needle arrangement and the injector body, the cylinder space, a gap between the second end of control piston and the injector body, and the discharge duct.