A connector for connecting a dialysate port of a dialyzer with a dialysate-carrying line and a dialyzer. The connector has a recess with a shift element on the end which accommodates the dialyzer port. The shift element is accommodated in the recess and is displaceable between a first position and a second position perpendicular to the direction of the lumen on the first end. The shift element does not pass through the lumen in the first position. In the second position, the lumen is constricted so that the connector with the shift element can be placed on the dialysate port and the connector locked on the dialysate port through engagement of the shift element behind an undercut on the port.