diff --git a/src/island_client.ml b/src/island_client.ml
index 75f0bf6..7f7a884 100644
--- a/src/island_client.ml
+++ b/src/island_client.ml
@@ -54,9 +54,13 @@ let init () =
   C2d.fill_rect context ~x:0. ~y:0. ~w:(float_of_int width)
     ~h:(float_of_int height)
 
-let tiles_per_w = width / tile_size
+let tiles_per_w =
+  let n = width / tile_size in
+  if n mod 2 = 0 then n - 1 else n
 
-let tiles_per_h = height / tile_size
+let tiles_per_h =
+  let n = height / tile_size in
+  if n mod 2 = 0 then n - 1 else n
 
 let orig_x = (width - (tiles_per_w * tile_size)) / 2