Mold base including a base wall and a peripheral side wall which is connected to the base wall by a fillet, this mould base ending with a peripheral upper edge and including ribs forming cavities for grooves for strengthening the base of a container to be formed and which each straddle the fillet, this mould base also including decompression vents hollowed out of the moulding face and which include, for each rib, at least one pair of shallow side channels which extend on either side of the rib and open, at an upper end, on to the peripheral upper edge.