A plug connection having two intermateable coupling parts that can be releasably locked via a locking device. The locking device includes a radial retaining bar on each of the coupling parts and a retaining part with a circumferentially closed annular contour. In a preassembled state, the retaining is undetachably assembled on one of the two coupling parts. In an assembled state, the retaining part axially and radially encompasses the retaining bars of both coupling parts. The retaining part includes an elastically moving retaining section having a C-shaped section defined by two collars. The collars have different sizes and/or shapes such that one collar releases an adjacent retaining bar upon the radial elastic outward movement out of the assembled state. The other collar remains engaged behind the retaining bar of the other coupling part.