diff --git a/src/visibility.rs b/src/visibility.rs
index b3dde56..2e26ca1 100644
--- a/src/visibility.rs
+++ b/src/visibility.rs
@@ -86,7 +86,7 @@ impl Viewshed {
                         } else {
                             let should_push = std::cell::RefCell::new(true);
                             let coord = Vec2::new(coord.x as f32 + 0.5, coord.y as f32 + 0.5);
-                            let dir = Dir2::new_unchecked((coord - *start).normalize());
+                            let dir = Dir2::new_unchecked((coord - *start).normalize_or_zero());
                             // println!("Casting from {coord} to {dir:?}");
                             spatial_query.cast_ray_predicate(
                                 *start,