diff --git a/Library/Homebrew/os/mac/version.rb b/Library/Homebrew/os/mac/version.rb
index 9a529df800..f48e38d470 100644
--- a/Library/Homebrew/os/mac/version.rb
+++ b/Library/Homebrew/os/mac/version.rb
@@ -4,6 +4,7 @@ module OS
   module Mac
     class Version < ::Version
       SYMBOLS = {
+        :sierra        => "10.12",
         :el_capitan    => "10.11",
         :yosemite      => "10.10",
         :mavericks     => "10.9",