diff --git a/Casks/vitalsource-bookshelf.rb b/Casks/vitalsource-bookshelf.rb
index 8515b3ecdca..a7c827c93de 100644
--- a/Casks/vitalsource-bookshelf.rb
+++ b/Casks/vitalsource-bookshelf.rb
@@ -1,6 +1,6 @@
 cask :v1 => 'vitalsource-bookshelf' do
 
-  if MacOS.release <= 10.7
+  if MacOS.release <= :lion
     version '6.5.2'
     sha256 'bf5873bb39ff76421a55c9ab769007bb1af64b21dabf6630a4087bbc29c27d55'
     url "http://downloads.vitalbook.com/vsti/bookshelf/#{version}/MAC/Bookshelf/VitalSource_Bookshelf_#{version}.zip"