I give arguments supporting the claim that one of the most prominent methodological results of French conventionalism – rejection of the possibility of a crucial experiment in mature empirical sciences – was formulated simultaneously by Pierre Duhem and Gaston Milhaud in 1894. Thus, I attempt to question the standard approach in philosophy and methodology of science, which attributes the said result exclusively to Duhem. I am building my case of Milhaud’s true contribution to the debate on the rejection of the existence of the experimentum crucis, made in his PhD thesis Essai sur les conditions et les limites de la certitude logique.