  Let $X$ be a locally finite preordered set, $\mathcal R$ a commutative ring
with identity and $I(X,\mathcal R)$ the incidence algebra of $X$ over $\mathcal
R$. In this note we prove that each Lie derivation of $I(X,\mathcal R)$ is
proper, provided that $\mathcal R$ is $2$-torsion free.
