diff --git a/src/xupnpd_http.lua b/src/xupnpd_http.lua
index cfe7f76..3599971 100644
--- a/src/xupnpd_http.lua
+++ b/src/xupnpd_http.lua
@@ -520,9 +520,11 @@ function http_handler(what,from,port,msg)
     -- Subtitle
     elseif url=='sub' then

-        local srt = "%s.srt":format(object)
+       local fmt = "%s.srt"
+       local srt = fmt:format(object)
        local pls=nil
-       object = "%s_":format(object)
+       fmt = "%s_"
+       object = fmt:format(object)
        while object:len() > 0 and (not pls or not pls.path) do
            object = object:gsub("_[^_]*$", "")
            pls=find_playlist_object(object)