An aircraft with at least one propulsion assembly and its fire-fighting system, which includes two reservoirs of extinguishing agent, and, associated with each reservoir, a control that can be actuated by a pilot to open the reservoir, a detection assembly to detect a fire and emit, if appropriate, a fire alert signal, the propulsion assembly including a first and a second compartment each including at least one fire zone, the fire-fighting system including a bypass valve controlled by a localization unit, a set of pipes connecting each reservoir to each of the fire zones through the bypass valve, the localization unit configured to detect a fire in a fire zone in the first compartment, and, if appropriate, control the bypass valve so it adopts a first state where the extinguishing agent in a reservoir is expelled towards the one or more fire zones in the first compartment after activation of the control associated with a reservoir, the bypass valve otherwise being controlled to adopt a second state, in which the extinguishing agent in a reservoir is expelled towards the one or more fire zones in the second compartment.