In this note, some discrepancies in the utilization of the Avrami model adopted for the crystallization modelling of advanced semicrystalline thermoplastic matrices are pointed out. In particular, the correct representation of the kinetic constants as a function of the isothermal crystallization temperature is discussed. In fact, Avrami analysis of isothermal crystallization data leads to the computation of kinetic constants characterized by physical dimensions depending on the calculated Avrami index. The representation on a single plot of these kinetic constants is not formally correct, and therefore a modification of the Avrami expression must be adopted.