--- a/terraform_gui.c	Thu Mar 30 15:47:18 2006 +0000
+++ b/terraform_gui.c	Thu Mar 30 19:16:44 2006 +0000
@@ -55,7 +55,7 @@
 	_generating_world = true;
 	BEGIN_TILE_LOOP(tile, size_x, size_y, TileXY(sx, sy)) {
 		if (GetTileType(tile) != MP_WATER) {
-			SetMapExtraBits(tile, (_ctrl_pressed) ? 0 : 1);
+			SetTropicZone(tile, (_ctrl_pressed) ? TROPICZONE_INVALID : TROPICZONE_DESERT);
 			DoCommandP(tile, 0, 0, NULL, CMD_LANDSCAPE_CLEAR);
 			MarkTileDirtyByTile(tile);
 		}