The invention concerns a timepiece including a case (10) and a crystal (22) together defining a housing (18) for a movement (20), and further including an element that is mobile in rotation (30) actuated by a control member (36) including a stem (42) of longitudinal axis AA, passing radially through said case (10), a crown (44) mounted on a first proximal end of said stem and a pinion (46) fixedly mounted in rotation on a second distal end of said stem (42). The control member (36) is fitted with a part (48) for axially securing said pinion (46) on said stem (42), arranged on the proximal side of said stem (42), said securing part (48) including: a first slit ring (62) mounted so as to be locked axially and radially on a first of the pinion (46)/stem (42) elements, and means for axially locking the second of the pinion (46)/stem (42) elements, secured to said slit ring (62).