  Let $R$ be a unital ring, let $E$ be a directed graph and recall that the
Leavitt path algebra $L_R(E)$ carries a natural $\mathbb{Z}$-gradation. We show
that $L_R(E)$ is strongly $\mathbb{Z}$-graded if and only if $E$ is row-finite,
has no sink, and satisfies Condition (Y). Our result generalizes a recent
result by Clark, Hazrat and Rigby, and the proof is short and self-contained.
