Abstract: The upper lock system of the passive door blade of a double door according to the invention comprises a bolt (19) arranged to be installed to the upper surface of the passive door blade and arranged to be controlled by means of a pull bar (9). The bolt is a part of the lock (18). The lock also has a power transmission connection part (23) for the interface part (17) of the upper lock system. The interface part comprises a grabber module (24), power transmission module (32, 34) and a spring (26). The grabber module (24) is arranged to linearly move between the extended position and the retracted position. A spring (26) is arranged to push the grabber module towards the extended position. The power transmission mechanism (32, 34) is operationally connected with the grabber module (4) and the power transmission connection part (23).