Electrical connector assembly, comprising: a plug connector, comprising: a connector housing having a flexible leg (11a, 11b) with primary locking means adapted to provide a primary locking function when the plug connector is mated with a corresponding counter connector, wherein the primary locking function can be unset when said flexible leg (11a, 11b) is flexed, and a secondary locking device being arranged movable relative to the connector housing between an open and a closed position, said device having a flexible arm and a jamming portion; wherein the flexible leg (11a, 11b) of the connector housing and the flexible arm of the secondary locking device are adapted to be in blocking contact when said flexible arm is not flexed, so as to inhibit movement of the secondary locking device from the open position into the closed position; wherein the flexible arm of the secondary locking device is adapted to be flexed when the plug connector is mated with the corresponding counter connector such that the secondary locking device can be moved into the closed position, and wherein when the secondary locking device is in the closed position the jamming portion of the secondary locking device is adapted to prevent a flexing of said flexible leg (11a, 11b); wherein the connector housing comprises guiding means adapted to guide the movement of the secondary locking device between the open and closed position such that the direction of movement is the same as the mating direction of the plug connector to the corresponding counter connector, characterized in that the guiding means comprises a recess or a gap and the corresponding wall of the secondary locking device comprises a step such that the secondary locking device can be rotated at least partially around an axis perpendicular to the mating direction so as to flex the flexible leg (11a, 11b) of the connector housing when the secondary locking device is rotated, whereby the step allows the rotation only when the locking device is pulled further outwards away from the open position. a plug connector, comprising: a connector housing having a flexible leg (11a, 11b) with primary locking means adapted to provide a primary locking function when the plug connector is mated with a corresponding counter connector, wherein the primary locking function can be unset when said flexible leg (11a, 11b) is flexed, and a secondary locking device being arranged movable relative to the connector housing between an open and a closed position, said device having a flexible arm and a jamming portion; a connector housing having a flexible leg (11a, 11b) with primary locking means adapted to provide a primary locking function when the plug connector is mated with a corresponding counter connector, wherein the primary locking function can be unset when said flexible leg (11a, 11b) is flexed, and a secondary locking device being arranged movable relative to the connector housing between an open and a closed position, said device having a flexible arm and a jamming portion; wherein the flexible leg (11a, 11b) of the connector housing and the flexible arm of the secondary locking device are adapted to be in blocking contact when said flexible arm is not flexed, so as to inhibit movement of the secondary locking device from the open position into the closed position; wherein the flexible arm of the secondary locking device is adapted to be flexed when the plug connector is mated with the corresponding counter connector such that the secondary locking device can be moved into the closed position, and wherein when the secondary locking device is in the closed position the jamming portion of the secondary locking device is adapted to prevent a flexing of said flexible leg (11a, 11b); wherein the connector housing comprises guiding means adapted to guide the movement of the secondary locking device between the open and closed position such that the direction of movement is the same as the mating direction of the plug connector to the corresponding counter connector, characterized in that the guiding means comprises a recess or a gap and the corresponding wall of the secondary locking device comprises a step such that the secondary locking device can be rotated at least partially around an axis perpendicular to the mating direction so as to flex the flexible leg (11a, 11b) of the connector housing when the secondary locking device is rotated, whereby the step allows the rotation only when the locking device is pulled further outwards away from the open position.