A nacelle for an aircraft propulsion assembly includes an actuator, a secondary door subject to the actuator and contributing to defining an external aerodynamic surface of the nacelle in a first position, a main door contributing to defining the external aerodynamic surface and including a recess that the actuator passes through in a deployed position but not in a retracted position, and a flap connected to the main door. The flap is movable between a closed position wherein the flap closes off at least a first region of the recess through which the actuator passes in the deployed position whereby the flap contributes to defining the external aerodynamic surface, and an open position wherein the flap is moved away from the recess so as to clear the passage for the actuator through the first region of the recess.