  Kerr black holes have their angular momentum, $J$, bounded by their mass,
$M$: $Jc\leqslant GM^2$. There are, however, known black hole solutions
violating this Kerr bound. We propose a very simple universal bound on the
rotation, rather than on the angular momentum, of four-dimensional, stationary
and axisymmetric, asymptotically flat black holes, given in terms of an
appropriately defined horizon linear velocity, $v_H$. The $v_H$ bound is simply
that $v_H$ cannot exceed the velocity of light. We verify the $v_H$ bound for
known black hole solutions, including some that violate the Kerr bound, and
conjecture that only extremal Kerr black holes saturate the $v_H$ bound.
