diff --git a/Casks/xamarin-android.rb b/Casks/xamarin-android.rb
index 708f5259b..dcc9d1aec 100644
--- a/Casks/xamarin-android.rb
+++ b/Casks/xamarin-android.rb
@@ -3,8 +3,8 @@ class XamarinAndroid < Cask
   sha256 '012f7266b123a1cc8cc189db8c3aea24c5daa8912df684525336fabc86e279e7'
 
   url "http://download.xamarin.com/MonoforAndroid/Mac/mono-android-#{version}.pkg"
-  # non-Sparkle appcast
-  appcast 'http://xamarin.com/installer_assets/v3/Mac/Universal/InstallationManifest.xml'
+  appcast 'http://xamarin.com/installer_assets/v3/Mac/Universal/InstallationManifest.xml',
+          :format => :unknown
   homepage 'http://xamarin.com/android'
   license :unknown