The system (10) for fixing a timepiece movement (2) to a watch case (30) element (3) includes at least one clamp (1), in particular at least two clamps, preferably three clamps or four clamps, which is intended to come into contact firstly with the movement and secondly with the watch case element, and a device (2a′; 3a′) for modifying the stiffness of the at least one clamp, particularly for modifying the bending stiffness of the at least one clamp, when the movement is fixed and/or displaced relative to the watch case element.