An elastomeric seal seals a pipe which is held in a push-in part of a plug-in coupling relative to a cylindrical interior surface of a housing of the plug-in coupling, into which the push-in part is pushed together with the pipe. The seal is in prestressed contact with the interior surface of the housing via an outward-facing annular lip and with the pipe via a radially inward-facing annular lip. The elastomeric seal is connectable by positive fitting to the push-in part, this positive fit being lockable by the assembly of the pipe to form a non-releasable connection, the pipe having a cylindrical and uninterrupted exterior circumference in the region of the seal. The joint between the seal and the push-in part is simple to assemble and is lockable by the insertion of the pipe. The connection of the seal to the push-in part may be additionally secured, with certain changes of diameter, by compression of the web-shaped connection between them.