An electrical connector assembly includes a plug with a plug body having a contact holder portion and an annular locking ring attached to the plug body. An elastic element holds the locking ring in a rest position. The locking ring has a first recess at a first end that creates a guide surface. The assembly also includes a mating connector having a plug-receiving portion configured to receive the contact holder portion of the plug. The plug-receiving portion includes a collar having a projection which, when mating the electrical plug and mating connector, engages the guide surface and rotates the locking ring. The locking ring has a second recess at a second end. The projection and the second recess are in a plane perpendicular to the plug-in axis in fully assembled state. The spring force rotates the locking ring and locks the plug body with the plug-receiving portion.