diff -r 37c99587825d -r 3078123e84ea rust/land2d/src/lib.rs
--- a/rust/land2d/src/lib.rs	Mon Nov 05 21:36:28 2018 +0100
+++ b/rust/land2d/src/lib.rs	Tue Nov 06 00:02:23 2018 +0100
@@ -133,7 +133,7 @@
         ) {
             let yd = y as isize + dir;
 
-            if land.is_valid_coordinate(0, yd as i32) {
+            if land.is_valid_y(yd as i32) {
                 stack.push((xl, xr, yd as usize, dir));
             }
         };