diff --git a/Casks/onyx.rb b/Casks/onyx.rb
index e37549c0cd16b..bd04dc908ecfb 100644
--- a/Casks/onyx.rb
+++ b/Casks/onyx.rb
@@ -14,8 +14,11 @@
     url 'http://www.titanium.free.fr/download/108/OnyX.dmg'
   elsif MacOS.version == :mavericks
     url 'http://www.titanium.free.fr/download/109/OnyX.dmg'
-  else
+  elsif MacOS.version == :yosemite
     url 'http://www.titanium.free.fr/download/1010/OnyX.dmg'
+  else
+    # Unusual case: there is no fall-through.  Each version of the software is
+    # specific to an OS X release, so define nothing when the release is unknown.
   end
   homepage 'http://www.titanium.free.fr/downloadonyx.php'
   license :unknown