The balance-spring (1) includes a plurality of coils (3) of which the end (6, 8) of the outer curve (2) is rigidified by deformation in order to define accurately the setting point (7) of said balance-spring, said deformation being able to be achieved by bending the end (6) of the outer curve (2) through 90.degree. in a plane perpendicular to the height of the balance-spring (1) or by folding down through 180.degree. a portion of the end (8) of the outer curve (2) against the inner or outer face of said end (2).
