Unused variable in gcc compiler

I have this code.

 for (int i = 0; i < n; i++) {
    Vertex v = *g->edges[i];
    int vIndex = find_index(g, n, followers, v);
    if (in_degrees[i] > out_degrees[i] && isReachable(g, src, v)) {
        followers[vIndex] = 1;
    }
}

I get Unused variable v even though the variable v is clearly being used!