diff --git a/docs/SPECIFICATION.md b/docs/SPECIFICATION.md
index 9a84fe6..6a87234 100644
--- a/docs/SPECIFICATION.md
+++ b/docs/SPECIFICATION.md
@@ -130,7 +130,7 @@ Solutions returned by the solver follow this format. You can load your map and s
 
 ## JS Visualiser
 
-For the [visualiser](https://www.cs.rochester.edu/u/kautz/sokoban/Sokoban.html) to work, puzzles must be rectangular. If your map is not rectangular, just filled it in with walls instead of empty spaces.
+For the [visualiser](https://web.archive.org/web/20210430155801/https://www.cs.rochester.edu/u/kautz/sokoban/Sokoban.html) to work, puzzles must be rectangular. If your map is not rectangular, just filled it in with walls instead of empty spaces.
 
 ![](./images/image03.png)