An expansion valve (1) for a vapour compression system, the valve (1) comprising a first valve part (5) having an outlet orifice (7) and a piston (8) movable inside the outlet orifice (7) in response to a differential pressure across the expansion valve (1), controlling a fluid flow through the first valve part (5). A cross-sectional flow area of the outlet orifice (7) between a circumference at an inner surface of the outlet orifice (7) and a circumference at an outer surface of the piston (8) varies as a function of the position of the piston (8) relative to the outlet orifice (7). A first cross-sectional flow area is defined at a first differential pressure, and a second cross-sectional flow area is defined at a second differential pressure, where the first cross-sectional flow area is smaller than the second cross-sectional flow area, and the first differential pressure is lower than the second differential pressure.