diff --git a/www/start_the_recording.lua b/www/start_the_recording.lua
index 7be289e..b0d8b1e 100644
--- a/www/start_the_recording.lua
+++ b/www/start_the_recording.lua
@@ -5,8 +5,8 @@ if not arg_output then
   return
 end
 
-if not (arg_output:gsub("[A-Za-z0-9_.]","")=="") then
-  ngx.say("Invalid query 'output'")
+if not (arg_output:gsub("[A-Za-z0-9_.-]","")=="") then
+  ngx.say("Invalid query 'output': '"..arg_output.."'")
   return
 end