--- a/main_gui.c	Sat Jul 16 20:58:04 2005 +0000
+++ b/main_gui.c	Sat Jul 16 23:47:37 2005 +0000
@@ -1218,7 +1218,7 @@
 	TileInfo ti;
 
 	FindLandscapeHeightByTile(&ti, tile);
-	if (ti.type != MP_CLEAR || (ti.tileh & 0x10))
+	if (IsTileType(tile, MP_CLEAR) || IsSteepTileh(ti.tileh))
 		return;
 
 	ModifyTile(tile, MP_SETTYPE(MP_UNMOVABLE) | MP_MAP5, 1);
@@ -1230,7 +1230,7 @@
 	TileInfo ti;
 
 	FindLandscapeHeightByTile(&ti, tile);
-	if (ti.type != MP_CLEAR || (ti.tileh & 0x10))
+	if (IsTileType(tile, MP_CLEAR) || IsSteepTileh(ti.tileh))
 		return;
 
 	ModifyTile(tile, MP_SETTYPE(MP_UNMOVABLE) | MP_MAP5, 0);