diff --git a/src/industry_map.h b/src/industry_map.h
--- a/src/industry_map.h
+++ b/src/industry_map.h
@@ -48,6 +48,7 @@ enum {
 	GFX_BUBBLE_CATCHER                 = 162,
 	GFX_TOFFEE_QUARY                   = 165,
 	GFX_SUGAR_MINE_SIEVE               = 174,
+	GFX_WATERTILE_SPECIALCHECK         = 255,  ///< not really a tile, but rather a very special check
 };
 
 /**