A chronograph mechanism including a zero-reset mechanism for resetting a chronograph counter to zero, including a zero-reset member and a hammer shaped to cooperate with the zero-reset member. The zero-reset member is a snail cam including a cam track extending in a spiral. The hammer can be displaced by the zero-reset control between a rest position in which the hammer is not in contact with the cam path and a zero-reset position in which the hammer is in contact with the cam path and holds the zero-reset member in the reference position, the hammer generating a driving torque on the zero-reset member between the rest position and the zero-reset position.