diff --git a/src/command.cpp b/src/command.cpp
--- a/src/command.cpp
+++ b/src/command.cpp
@@ -455,13 +455,17 @@ bool DoCommandP(TileIndex tile, uint32 p
 	 * restrictions which may cause the test run to fail (the previous
 	 * road fragments still stay there and the town won't let you
 	 * disconnect the road system), but the exec will succeed and this
-	 * fact will trigger an assertion failure. --pasky */
+	 * fact will trigger an assertion failure. --pasky
+	 * CMD_CLONE_VEHICLE: You can only refit vehicles once they have been
+	 * bought, so you can't estimate the cost of cloning if the vehicle to be
+	 * cloned has been refitted. */
 	notest =
 		(cmd & 0xFF) == CMD_CLEAR_AREA ||
 		(cmd & 0xFF) == CMD_CONVERT_RAIL ||
 		(cmd & 0xFF) == CMD_LEVEL_LAND ||
 		(cmd & 0xFF) == CMD_REMOVE_ROAD ||
-		(cmd & 0xFF) == CMD_REMOVE_LONG_ROAD;
+		(cmd & 0xFF) == CMD_REMOVE_LONG_ROAD ||
+		(cmd & 0xFF) == CMD_CLONE_VEHICLE;
 
 	_docommand_recursive = 1;