For thermodynamic conditions lying in the non-classical regime, the non-monotone evolution of the Mach number in isentropic expansions can be found even in subsonic conditions. In fact, for values of Γ Γ < 0 , positive values of J can be reached also in subsonic flows ( M < 1 ). In other words, the non-monotone Mach number evolution is also possible in the convergent section of an isentropic nozzle.