  The influence of weak localization on Hanle effect in a two-dimensional
system with spin-split spectrum is considered. We show that weak localization
drastically changes the dependence of stationary spin polarization $\mathbf S$
on external magnetic field $B.$ In particular, the non-analytic dependence of
$\mathbf S$ on $\mathbf B$ is predicted for III-V-based quantum wells grown in
[110] direction and for [100]-grown quantum wells having equal strengths of
Dresselhaus and Bychkov-Rashba spin-orbit coupling. It is shown that in weakly
localized regime the components of $\mathbf S$ are discontinuous at $B=0.$ At
low $B,$ the magnetic field-induced rotation of the stationary polarization is
determined by quantum interference effects. This implies that the Hanle effect
in such systems is totally driven by weak localization.
