diff --git a/Casks/opacity.rb b/Casks/opacity.rb
index 8e0b3d4e01d..38270a6d8c7 100644
--- a/Casks/opacity.rb
+++ b/Casks/opacity.rb
@@ -4,6 +4,8 @@ cask :v1 => 'opacity' do
 
   url 'http://downloads.likethought.com/opacity.zip'
   name 'Opacity'
+  appcast 'http://downloads.likethought.com/appcasts/opacity.php',
+          :sha256 => '031a196c3a9fb04b1eb31d791b154bed797a043621b8350d85eca73c113c2fe0'
   homepage 'http://likethought.com/opacity/'
   license :unknown    # todo: change license and remove this comment; ':unknown' is a machine-generated placeholder