  We present a calculation of the spin polarization of spin-1/2 fermions in a
relativistic fluid at local thermodynamic equilibrium at the second order in
the gradient expansion, including second-order derivatives. The second-order
derivative terms vanish if the local equilibrium hypersurface is the hyperplane
$t=const$ in the collision center-of-mass frame. However, since the freeze-out
hypersurface has a non-trivial space-time structure, these terms may result in
a non-vanishing contribution to the spin polarization, whose magnitude needs to
be assessed with numerical computations.
