diff --git a/src/map.h b/src/map.h
index b977eaa7b..296b8d7e7 100644
--- a/src/map.h
+++ b/src/map.h
@@ -314,8 +314,8 @@ static inline WZ_DECL_PURE MAPTILE *mapTile(SDWORD x, SDWORD y)
 	ASSERT(y >= -1, "mapTile: y value is too small (%d,%d) in %dx%d",x,y,mapWidth,mapHeight);
 	x = (x < 0 ? 0 : x);
 	y = (y < 0 ? 0 : y);
-	ASSERT(x < world_coord(mapWidth)+TILE_UNITS, "mapTile: x value is too big (%d,%d) in %dx%d",x,y,mapWidth,mapHeight);
-	ASSERT(y < world_coord(mapHeight)+TILE_UNITS, "mapTile: y value is too big (%d,%d) in %dx%d",x,y,mapWidth,mapHeight);
+	ASSERT(x < mapWidth + 1, "mapTile: x value is too big (%d,%d) in %dx%d",x,y,mapWidth,mapHeight);
+	ASSERT(y < mapHeight + 1, "mapTile: y value is too big (%d,%d) in %dx%d",x,y,mapWidth,mapHeight);
 	x = (x >= mapWidth ? mapWidth - 1 : x);
 	y = (y >= mapHeight ? mapHeight - 1 : y);