Plug-in coupling for fluid lines, comprising at least one female line portion, which is made substantially of plastic and into which a male line portion is able to be plugged in a sealing manner, and at least one resilient locking device, by means of which the line portions (1, 12) are able to be locked together and unlocked from one another, wherein the device has at least one spring blocking element and the female line portion has blocking openings which correspond to the at least one spring blocking element, the female line portion has in the region of the blocking openings at least one reinforcement made of a metallic material, characterized in that the at least one metallic reinforcement is in the form of a ring which is arranged around the female line portion in the region of the blocking openings, wherein the metallic ring has apertures which correspond to the blocking openings such that the spring blocking element, with the coupling fully assembled, can engage both through the apertures in the metallic ring and through the blocking openings, wherein - the metallic ring is in the form of a split spring ring and the female line portion has ring webs which are spaced axially apart from one another and between which the split spring ring is able to be positioned such that the spring ring is fixed axially to the female line portion, or - the metallic ring is in the form of a closed ring with a predetermined diameter, wherein the closed ring is embedded in the plastic of the female line portion. at least one female line portion, which is made substantially of plastic and into which a male line portion is able to be plugged in a sealing manner, and at least one resilient locking device, by means of which the line portions (1, 12) are able to be locked together and unlocked from one another, wherein the device has at least one spring blocking element and the female line portion has blocking openings which correspond to the at least one spring blocking element, the female line portion has in the region of the blocking openings at least one reinforcement made of a metallic material, characterized in that the at least one metallic reinforcement is in the form of a ring which is arranged around the female line portion in the region of the blocking openings, wherein the metallic ring has apertures which correspond to the blocking openings such that the spring blocking element, with the coupling fully assembled, can engage both through the apertures in the metallic ring and through the blocking openings, wherein - the metallic ring is in the form of a split spring ring and the female line portion has ring webs which are spaced axially apart from one another and between which the split spring ring is able to be positioned such that the spring ring is fixed axially to the female line portion, or - the metallic ring is in the form of a closed ring with a predetermined diameter, wherein the closed ring is embedded in the plastic of the female line portion. - the metallic ring is in the form of a split spring ring and the female line portion has ring webs which are spaced axially apart from one another and between which the split spring ring is able to be positioned such that the spring ring is fixed axially to the female line portion, or - the metallic ring is in the form of a closed ring with a predetermined diameter, wherein the closed ring is embedded in the plastic of the female line portion.