diff --git a/rail_cmd.c b/rail_cmd.c
--- a/rail_cmd.c
+++ b/rail_cmd.c
@@ -840,7 +840,7 @@ int32 CmdRenameWaypoint(int x, int y, ui
 	StringID str;
 
 	if (_decode_parameters[0] != 0) {
-		str = AllocateNameUnique((byte*)_decode_parameters, 0);
+		str = AllocateNameUnique((const char*)_decode_parameters, 0);
 		if (str == 0) return CMD_ERROR;
 
 		if (flags & DC_EXEC) {