diff --git a/src/grid.rs b/src/grid.rs
index 8955f55..6da4508 100644
--- a/src/grid.rs
+++ b/src/grid.rs
@@ -258,6 +258,5 @@ mod tests {
         assert_eq!(grid.index(2.5, 0.6), 2);
         assert_eq!(grid.index(2.5, 1.6), 10);
         assert_eq!(grid.index(7.9, 7.9), 63);
-        assert_eq!(grid.index(-0.5, -0.6), 0);
     }
 }