A pump having an adjustable delivery volume, including: a pump housing featuring a delivery chamber which includes a delivery chamber inlet for a fluid and a delivery chamber outlet for the fluid; a delivery member, which can be rotated within the delivery chamber, for delivering the fluid; an adjusting device featuring a setting structure, which is mounted such that it can move back and forth within the pump housing in order to adjust the delivery volume of the pump, and a helical spring for applying a spring force, which acts in a setting direction, to the setting structure, wherein the windings of the helical spring are enclosed by an envelope lying on the outside of the helical spring wherein the cross-sectional area of the envelope as measured transversely with respect to the longitudinal direction of the spring changes progressively in the longitudinal direction of the spring.