--- a/src/terraform_cmd.cpp	Sun Nov 16 13:49:57 2008 +0000
+++ b/src/terraform_cmd.cpp	Sun Nov 16 14:17:49 2008 +0000
@@ -359,6 +359,7 @@
 
 	/* Check range of destination height */
 	if (h > MAX_TILE_HEIGHT) return_cmd_error((oldh == 0) ? STR_1003_ALREADY_AT_SEA_LEVEL : STR_1004_TOO_HIGH);
+	if (p2 == 0) _error_message = STR_ALREADY_LEVELLED;
 
 	/* make sure sx,sy are smaller than ex,ey */
 	int ex = TileX(tile);