Most recent Martian interior structure models are based on the planet's polar moment of inertia C, although the mean moment of inertia I is required for constructing spherically symmetric models of planetary interiors. Using the improved value of C/MpRp2 recently obtained from a combined reanalysis of the entire set of radio science data collected during the last three decades and accounting for the rotationally and topographically induced shape of the planet's gravitational field, we find a mean moment-of-inertia factor of I/MpRp2 = 0.3635 ¿ 0.0012. The new lower value suggests a core radius several tens of kilometers larger if other parameters like core density, crust density, and crust thickness are fixed. It further implies that the Martian crust is several tens of kilometers thicker than previously thought if crust and mantle densities and core size are given. Moreover, the Martian mantle may be less dense, about several tens of kg m-3, with a smaller iron content than previously thought if crust thickness and core size are specified. The mantle density of Mars is relatively well determined by the planet's moment of inertia factor if crust thickness and density are specified.