The timepiece movement includes a balance-and-hairspring oscillator and an escapement cooperating with the oscillator. The outer turn of the hairspring includes a stiffened portion (9″) arranged to at least partially compensate for the variation in the rate of the movement in dependence upon the oscillation amplitude of the balance caused by the escapement. The hairspring further includes at least one of the following features: a) a distance (R′) between the inner end of the hairspring and the centre of rotation of the hairspring lower than 400 μm, b) a Grossmann curve (10) defined by the inner turn of the hairspring, c) a stiffened portion defined by the inner turn of the hairspring.