An electrical plug-in connector with a casing, with a lever rotatably mounted on the casing, - the casing having a flexible blocking element (26, 27), - the blocking element (26, 27) having an actuating surface, - the lever having a blocking surface, - the blocking element (26, 27) having a second blocking surface, with, in a rest position of the lever and in a rest position of the blocking element (26, 27), the second blocking surface of the blocking element (26, 27) being associated with the blocking surface of the lever and blocking a movement of the lever from the rest position into an end position, characterized by - the lever having a guideway (30, 31), the guideway (30, 31) being provided for guiding a guide element (54, 55) of a second casing, - an insertion space (24, 25) for introducing the guide element (54, 55) into the guideway (30, 31) being provided, - the actuating surface in a rest position of the blocking element (26, 27) projecting into the insertion space (24, 25), - with the guide element (54, 55) being guided in the guideway (30, 31) upon rotation of the lever and the second casing being pulled from a pre-assembly position with regard to the casing into an end position, - the blocking element (26, 27) being formed such that the guide element (54, 55) upon introduction of the second casing into the pre-assembly position in relation to the casing being guided into the insertion space (24, 25) and in so doing the guide element (54, 55) acting on the actuating surface such that the blocking element (26, 27) is moved into a release position, - so that the position of the second blocking surface of the blocking element (26, 27) relative to the blocking surface of the lever is changed such that the lever is released for a movement into the end position. - the casing having a flexible blocking element (26, 27), - the blocking element (26, 27) having an actuating surface, - the lever having a blocking surface, - the blocking element (26, 27) having a second blocking surface, with, in a rest position of the lever and in a rest position of the blocking element (26, 27), the second blocking surface of the blocking element (26, 27) being associated with the blocking surface of the lever and blocking a movement of the lever from the rest position into an end position, - the lever having a guideway (30, 31), the guideway (30, 31) being provided for guiding a guide element (54, 55) of a second casing, - an insertion space (24, 25) for introducing the guide element (54, 55) into the guideway (30, 31) being provided, - the actuating surface in a rest position of the blocking element (26, 27) projecting into the insertion space (24, 25), - with the guide element (54, 55) being guided in the guideway (30, 31) upon rotation of the lever and the second casing being pulled from a pre-assembly position with regard to the casing into an end position, - the blocking element (26, 27) being formed such that the guide element (54, 55) upon introduction of the second casing into the pre-assembly position in relation to the casing being guided into the insertion space (24, 25) and in so doing the guide element (54, 55) acting on the actuating surface such that the blocking element (26, 27) is moved into a release position, - so that the position of the second blocking surface of the blocking element (26, 27) relative to the blocking surface of the lever is changed such that the lever is released for a movement into the end position.