II law of thermodynamics & polytropic process

The polytropic process is defined as such that $pV^m=A$, where $A$ is a constant. Generally, the change in entropy is
$$Delta S=nR ln frac{V}{V_0}+nC_Vln frac{T}{T_0}.$$
Using $pV=nRT$ and $pV^m=A$ we get $T=frac{AV^{1-m}}{nR}$. Substituting into previous equation we obtain:
$$Delta S=(gamma -m)C_Vnln frac{V}{V_0},$$
which is the formula for $Delta S$ in polytropic process and $gamma=C_p/C_V$. According to Wikipedia, for $m < 0$ II law of thermodynamics would be violated. The problem is, I can’t really see why it would be – the entropy is positive and everything seems fine…