diff --git a/bot/utils.lua b/bot/utils.lua
index efd8ccb..1ddb1c4 100644
--- a/bot/utils.lua
+++ b/bot/utils.lua
@@ -46,7 +46,10 @@ function get_http_file_name(url, headers)
   content_type = content_type or headers["Content-type"]
   content_type = content_type or h["Content-Type"]
   
-  local extension = mimetype.get_mime_extension(content_type)
+  local extension = nil
+  if content_type then
+    extension = mimetype.get_mime_extension(content_type)
+  end
   if extension then
     file_name = file_name.."."..extension
   end