  In connection with a recent experiment [Russo {\it et al.}, Phys. Rev. Lett.
{\bf 95}, 027002 (2005)], we investigate the effect of weak localization on non
local transport in normal metal / insulator / superconductor / insulator /
normal metal (NISIN) trilayers, with extended interfaces. The negative weak
localization contribution to the crossed resistance can exceed in absolute
value the positive elastic cotunneling contribution if the normal metal phase
coherence length or the energy are large enough.
