diff --git a/station_cmd.c b/station_cmd.c
--- a/station_cmd.c
+++ b/station_cmd.c
@@ -1360,7 +1360,7 @@ int32 CmdBuildRoadStop(TileIndex tile, u
 	bool type = !!p2;
 
 	/* Saveguard the parameters */
-	if (p1 > 3) return CMD_ERROR;
+	if (!IsValidDiagDirection(p1)) return CMD_ERROR;
 
 	SET_EXPENSES_TYPE(EXPENSES_CONSTRUCTION);