A fail-safe actuator for moving a part between two end positions, comprising: a first drive, a first drive train which can be set in motion by the first drive which has a first output shaft which transmits the movement of the actuator outwards in the direction of the part, a second drive, a second drive train which can be set in motion by the second drive which has a second output shaft which runs coaxially with the first output shaft, wherein the first and/or the second drive (18, 118) can be activated, selectively, in order to set the first and/or second output shaft (34, 38) in motion, an energy storage device, optionally comprising at least one elastic spring element, which is coupled with the second drive train, at least one externally actuatable holding device which ensures, selectively, that the energy stored in the energy storage device remains in the energy storage device or is released to the second drive train, a mechanical rotary entrainment device between the second output shaft and the first output shaft which is configured such that it permits a rotation of the first output shaft relative to the second output shaft by at least one angle of rotation which is associated with the distance between the end positions if the energy storage device is not released and if the drive moves the first output shaft between the end positions; and provides a rotary entrainment of the first output shaft by the second output shaft with the energy storage device released and the failed drive in a first of the two end positions; characterised in that the first and the second output shaft (34, 38) are coupleable in the direction of rotation by means of stop surfaces (90, 92, 94, 96) which come into contact with one another. a first drive, a first drive train which can be set in motion by the first drive which has a first output shaft which transmits the movement of the actuator outwards in the direction of the part, a second drive, a second drive train which can be set in motion by the second drive which has a second output shaft which runs coaxially with the first output shaft, wherein the first and/or the second drive (18, 118) can be activated, selectively, in order to set the first and/or second output shaft (34, 38) in motion, an energy storage device, optionally comprising at least one elastic spring element, which is coupled with the second drive train, at least one externally actuatable holding device which ensures, selectively, that the energy stored in the energy storage device remains in the energy storage device or is released to the second drive train, a mechanical rotary entrainment device between the second output shaft and the first output shaft which is configured such that it permits a rotation of the first output shaft relative to the second output shaft by at least one angle of rotation which is associated with the distance between the end positions if the energy storage device is not released and if the drive moves the first output shaft between the end positions; and provides a rotary entrainment of the first output shaft by the second output shaft with the energy storage device released and the failed drive in a first of the two end positions; permits a rotation of the first output shaft relative to the second output shaft by at least one angle of rotation which is associated with the distance between the end positions if the energy storage device is not released and if the drive moves the first output shaft between the end positions; and provides a rotary entrainment of the first output shaft by the second output shaft with the energy storage device released and the failed drive in a first of the two end positions; characterised in that the first and the second output shaft (34, 38) are coupleable in the direction of rotation by means of stop surfaces (90, 92, 94, 96) which come into contact with one another.