A motor vehicle chassis includes two lateral floor supports and a seat-cushion support part positioned between two lateral raisers fixed on top of the lateral floor supports and assembled with the lateral floor supports. The chassis further includes two seat-cushion support reinforcements each assembled with a lateral floor support and with a lateral raiser, each seat-cushion support reinforcement including: a substantially horizontal plate extending the seat-cushion support part laterally, assembled with the lateral raiser along a substantially vertical mating edge of the plate, and a single support leg extending downwards from the plate, assembled with the lateral floor support, and the assembly end of which is positioned vertically below the plate, some distance from a projection onto the horizontal of the mating edge.