Capacitance, pyroelectric and electrooptical measurements have been carried out over a certain temperature range near the smectic A-C* phase transition for a Chisso compound showing the sign inversion of the spantaneous polarization with temperature. Two Landau expansion coefficients, namely, the polarization-to-tilt coupling constant C and the tilt elastic coefficient cc have been calculated. Coefficient a is close to that known for conventional ferroelectric liquid crystals (e.g., DOBAMBC), coefficient C manifests nonmonotonic temperature dependence with a maximum well above the A-C* transition and an inflection point at the transition. This behaviour may qualitatively be understood if the biaxiality induced by a molecular tilt is taken into account.