Let $V$ be a paracompact strictly $K$-analytic space, $L$ a line bundle on $V$ and $({\mathfrak{V}},{\mathfrak{L}})$ a formal model of $(V,L)$. Let $F$ be a non-archimedean extension of $K$ and $({\mathfrak{V}}_{F},{\mathfrak{L}}_{F})$ the model of $(V_{F},L_{F})$ obtained by base change. Then ${\mathfrak{L}}$ is nef if and only if ${\mathfrak{L}}_{F}$ is nef.