A plug-in coupling for connecting a fluid line with a pipe having a circumferential holding rib includes a pipe piece with a first end portion connectable to the fluid line and a second end portion which can be plugged together with the pipe, wherein the second end portion is connectable to a first coupling ring part of a coupling ring and is connected through elastic holding arms to a non-circular elastically expandable second coupling ring part. The second coupling ring part has locking sections which are distributed over a predetermined circumferential angle range of a circumference of the pipe piece. When the pipe and pipe piece are plugged together, the locking sections slide over the holding rib and expand the second coupling ring part and engage behind the holding rib, wherein the components located between the locking sections of the second coupling ring part are arched outwardly. The second coupling ring part has at least three locking sections and the circumferential angle range is greater than 180°, wherein the outwardly arched parts protrude beyond the circumscribed circle of the locking projections.