The disclosure relates to a modular plug connector comprising a metal housing and an insulating holding frame received therein. At least one plug connector module is received in the holding frame, comprises a metallic or at least electrically conductive material, and is electrically insulated from the housing by the holding frame. Furthermore, an earthing device, which bridges the holding frame and permits an electrical contact between the plug connector module and the metal housing, is provided on the plug connector module. This allows different plug connector modules to be held in the holding frame insulated from the housing, and at the same time others to be held in electrical contact with the housing.