The disclosure relates to a modular plug connector which has a plug comprising a plurality of plug modules and has a mating plug comprising a plurality of mating plug modules, in which each plug module forms a plug module pair with a mating plug module, wherein the plug and the mating plug can assume an interconnected state and wherein at least one of the plug module pairs has at least one locking device, which can assume a locking state in the interconnected state of the plug and the mating plug, in which locking state the locking device prevents the plug module and the mating plug module of said plug module pair from separating from each other.