Abstract: The invention relates to a locking system for a plug coupling device and to a plug coupling device having a housing in which the locking system according to the invention is arranged. A plug having a projection, which may for example be a guide pin of a commercially available safety plug, can be coupled to the plug coupling device by means of the locking system according to the invention, wherein a locking device in the form of a slider engages behind the projections of the plug such that the plug coupled to the plug coupling device cannot be removed from the plug coupling device. In addition, the locking device being in the locking position prevents an unauthorised insertion of a plug into the plug coupling device.