/* test non-manifold cases */
if(!can_add_face(index, num)) {
/* we could try to add face in opposite winding instead .. */
- fprintf(stderr, "Warning: non manifold mesh, invalid face '%lu'.\n", faces.size());
+ fprintf(stderr, "Warning: non manifold mesh, invalid face '%lu'.\n", (unsigned long)faces.size());
return NULL;
}