A device (6) for autonomous adjustment of the active length of a spiral (5), for oscillators (4, 5) of the balance-spiral type, comprising a cock (12) mounted on a plate (13) of a horological movement (2) and in which a balance shaft pivots, the spiral (5) including an inner end secured to the balance shaft and an outer end secured to a balance spring stud (8) fastened to a balance spring stud holder (10), the balance spring stud holder (10) being pivotably mounted on the cock (12) concentrically to the balance shaft, and means for modifying the active length of the spiral (5).