We assume that for all $d \geqslant 0$, $\mathbb{P}(X \in d\mathbb{Z}) < 1$, and that $g$ is of class $\mathscr{C}^1$, with support in $[0, K]$ with $K > 0$. We admit that $\lim_{x \rightarrow +\infty} \inf_{t \geqslant x} f'(t) = 0$. Deduce that $f'(t) \rightarrow 0$ when $t \rightarrow +\infty$.