A timepiece wheel governor for regulating the pivoting speed (ω) of a wheel set, about a pivot axis, including a pivoting inertia-block. It includes a spring to return this block towards this axis, and, when the wheel set pivots at a lower speed than a reference speed (ωc), this block remains confined within a first volume of revolution, and, when the wheel set pivots at a higher speed than the reference speed (ωc), this block is engaged, in one peripheral portion thereof, in a second volume contiguous with and external to the first one, this peripheral portion cooperating in this second volume with a regulator arranged to brake the wheel set and return the pivoting speed (ω) thereof to the reference speed (ωc), and to dissipate the surplus energy.