Disclosed is a method and device for guiding an aircraft flying along a flight trajectory. The flight trajectory has at least one constrained section, and the aircraft flies at a required speed within the constrained section to comply with a required arrival time at a predetermined waypoint in the constrained section. Auxiliary speed setpoints are determined to guide the aircraft to arrive at an auxiliary arrival tune at an auxiliary waypoint, with the auxiliary speed setpoints being applied by a guidance system to guide the aircraft.