diff --git a/Casks/all2mp3.rb b/Casks/all2mp3.rb
index 0613712edc0..43c844170b5 100644
--- a/Casks/all2mp3.rb
+++ b/Casks/all2mp3.rb
@@ -5,6 +5,7 @@ class All2mp3 < Cask
   url 'http://www.tresrrr.com/Program/All2MP3.zip'
   appcast 'http://www.tresrrr.com/All2MP3/Appcast.xml'
   homepage 'http://www.tresrrr.com/All2MP3/ENGLISH.html'
+  license :unknown
 
   app 'All2MP3.app'
 end