diff --git a/window.c b/window.c
--- a/window.c
+++ b/window.c
@@ -1,6 +1,7 @@
 #include "stdafx.h"
 #include "openttd.h"
 #include "debug.h"
+#include "functions.h"
 #include "map.h"
 #include "player.h"
 #include "window.h"