Lemma 21.15.2. Let $f : (\mathop{\mathit{Sh}}\nolimits (\mathcal{C}), \mathcal{O}_\mathcal {C}) \to (\mathop{\mathit{Sh}}\nolimits (\mathcal{D}), \mathcal{O}_\mathcal {D})$ be a morphism of ringed topoi. If $f$ is flat, then $f_*\mathcal{I}$ is an injective $\mathcal{O}_\mathcal {D}$-module for any injective $\mathcal{O}_\mathcal {C}$-module $\mathcal{I}$.

**Proof.**
In this case the functor $f^*$ is exact, see Modules on Sites, Lemma 18.30.2. Hence the result follows from Homology, Lemma 12.26.1.
$\square$

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