An assembly for holding or supporting a timepiece balance spring includes a balance spring stud and a stud-holder. The stud-holder includes a device to secure the stud-holder to an escapement mechanism. The balance spring stud includes a lateral bearing surface defining a direction of holding or supporting the balance spring. The stud-holder is in two parts, and includes a rigid structure carrying the securing device, and a strip spring pressed against this rigid structure and including at least one elastic lip defining, with this structure, a chamber for receiving this stud and cooperating with this lateral bearing surface of this stud to hold this stud in an indexed locking position.