An intake manifold for an internal combustion engine comprising an engine head in which there are obtained a number of cylinders; the intake manifold comprises a central body, wherein there are obtained an intake chamber which receives the intake air and a number of conduits each of which connects the chamber to a corresponding cylinder of the internal combustion engine; first passage through holes obtained in the central body for fastening the intake manifold to the engine head by means of first fastening screws screwed into the engine head; a common rail which receives the pressurized fuel and is connected to a number of injectors, each of which injects the fuel into a corresponding cylinder; second blank threaded fastening holes obtained in the central body for fastening the common rail to the central body itself by means of the second fastening screws screwed into the central body and, for each second fastening hole, a metallic reinforcement bracket, which presents a first assembly through hole arranged over and coaxially to a corresponding first fastening hole in order to be locked onto the central body by the corresponding first fastening screw and a second assembly through hole arranged over and coaxially to a corresponding second fastening hole in order to be locked onto the central body of the corresponding second fastening screw.