An exhaust turbocharger includes an air-guiding section. A spiral channel is formed downstream of a wheel chamber in the air-guiding section. Between the wheel chamber and the spiral channel, a diffuser channel is formed in the air-guiding section. Upstream of the wheel chamber, an inlet channel is formed in the air-guiding section for the inflow of fluid to be compressed. In the inlet channel, a cross-section-changing unit. The cross-section-changing unit comprises an operating element with at least two movable element parts to produce a baffle which can protrude, with the aid of an adjusting unit, into the inlet cross-section rotationally and/or in a translational manner or can be removed from the inlet cross-section. The two element parts are fixedly disposed at one element end jointly in the air-guiding section. A relative movement of the element parts can be brought about in particular in an opposing direction.