A method and device checks the conformity of a trajectory calculated by a flight management system of an aircraft in relation to reference data comprising a reference map. The method includes: geo-referencing of a reference map; determination of a reference trajectory from the geo-referenced reference map; detection of nonconformity in the trajectory calculated by the flight management system by comparison of the trajectory calculated by the flight management system with the reference trajectory; and emission of a warning if a nonconformity is detected.