diff --git a/Library/Homebrew/extend/ENV/std.rb b/Library/Homebrew/extend/ENV/std.rb
index 03273fc888..09c36ae68e 100644
--- a/Library/Homebrew/extend/ENV/std.rb
+++ b/Library/Homebrew/extend/ENV/std.rb
@@ -224,7 +224,7 @@ module Stdenv
   end
 
   def macosxsdk version=MacOS.version
-    return unless MACOS
+    return unless OS.mac?
     # Sets all needed lib and include dirs to CFLAGS, CPPFLAGS, LDFLAGS.
     remove_macosxsdk
     version = version.to_s
diff --git a/Library/Homebrew/formula_installer.rb b/Library/Homebrew/formula_installer.rb
index f09a2d6eb2..a7b233cf39 100644
--- a/Library/Homebrew/formula_installer.rb
+++ b/Library/Homebrew/formula_installer.rb
@@ -384,7 +384,7 @@ class FormulaInstaller
       link
     end
 
-    fix_install_names
+    fix_install_names if OS.mac?
 
     record_cxx_stdlib
 
diff --git a/Library/Homebrew/global.rb b/Library/Homebrew/global.rb
index 36e5cf992a..dc809021d0 100644
--- a/Library/Homebrew/global.rb
+++ b/Library/Homebrew/global.rb
@@ -5,6 +5,7 @@ require 'extend/ARGV'
 require 'extend/string'
 require 'extend/symbol'
 require 'extend/enumerable'
+require 'os'
 require 'utils'
 require 'exceptions'
 require 'set'
@@ -72,11 +73,9 @@ if RUBY_PLATFORM =~ /darwin/
   MACOS_FULL_VERSION = `/usr/bin/sw_vers -productVersion`.chomp
   MACOS_VERSION = MACOS_FULL_VERSION[/10\.\d+/].to_f
   OS_VERSION = "Mac OS X #{MACOS_FULL_VERSION}"
-  MACOS = true
 else
   MACOS_FULL_VERSION = MACOS_VERSION = 0
   OS_VERSION = RUBY_PLATFORM
-  MACOS = false
 end
 
 HOMEBREW_GITHUB_API_TOKEN = ENV["HOMEBREW_GITHUB_API_TOKEN"]
diff --git a/Library/Homebrew/hardware.rb b/Library/Homebrew/hardware.rb
index 44642d44fe..0a52d10dbc 100644
--- a/Library/Homebrew/hardware.rb
+++ b/Library/Homebrew/hardware.rb
@@ -1,3 +1,5 @@
+require 'os'
+
 class Hardware
   module CPU extend self
     INTEL_32BIT_ARCHS = [:i386].freeze
@@ -30,11 +32,10 @@ class Hardware
     end
   end
 
-  case RUBY_PLATFORM.downcase
-  when /darwin/
+  if OS.mac?
     require 'os/mac/hardware'
     CPU.extend MacCPUs
-  when /linux/
+  elsif OS.linux?
     require 'os/linux/hardware'
     CPU.extend LinuxCPUs
   else
diff --git a/Library/Homebrew/keg_fix_install_names.rb b/Library/Homebrew/keg_fix_install_names.rb
index c9ff7b4bc9..694daaba8a 100644
--- a/Library/Homebrew/keg_fix_install_names.rb
+++ b/Library/Homebrew/keg_fix_install_names.rb
@@ -1,6 +1,5 @@
 class Keg
   def fix_install_names options={}
-    return unless MACOS
     mach_o_files.each do |file|
       install_names_for(file, options) do |id, bad_names|
         file.ensure_writable do
diff --git a/Library/Homebrew/macos.rb b/Library/Homebrew/macos.rb
index b3e4b6452b..1caaa8b43d 100644
--- a/Library/Homebrew/macos.rb
+++ b/Library/Homebrew/macos.rb
@@ -253,7 +253,7 @@ module MacOS extend self
   end
 
   def mdfind id
-    return [] unless MACOS
+    return [] unless OS.mac?
     (@mdfind ||= {}).fetch(id.to_s) do |key|
       @mdfind[key] = `/usr/bin/mdfind "kMDItemCFBundleIdentifier == '#{key}'"`.split("\n")
     end
diff --git a/Library/Homebrew/os.rb b/Library/Homebrew/os.rb
new file mode 100644
index 0000000000..e16c81c7de
--- /dev/null
+++ b/Library/Homebrew/os.rb
@@ -0,0 +1,9 @@
+module OS
+  def self.mac?
+    /darwin/i === RUBY_PLATFORM
+  end
+
+  def self.linux?
+    /linux/i === RUBY_PLATFORM
+  end
+end
diff --git a/Library/Homebrew/os/mac/xcode.rb b/Library/Homebrew/os/mac/xcode.rb
index 1279be1d1f..0472f73ab5 100644
--- a/Library/Homebrew/os/mac/xcode.rb
+++ b/Library/Homebrew/os/mac/xcode.rb
@@ -84,7 +84,7 @@ module MacOS::Xcode extend self
     # This is a separate function as you can't cache the value out of a block
     # if return is used in the middle, which we do many times in here.
 
-    return "0" unless MACOS
+    return "0" unless OS.mac?
 
     # this shortcut makes version work for people who don't realise you
     # need to install the CLI tools
diff --git a/Library/Homebrew/test/testing_env.rb b/Library/Homebrew/test/testing_env.rb
index 9bc5d871fb..a7b25aa200 100644
--- a/Library/Homebrew/test/testing_env.rb
+++ b/Library/Homebrew/test/testing_env.rb
@@ -29,7 +29,6 @@ HOMEBREW_VERSION       = '0.9-test'
 RUBY_BIN = Pathname.new(RbConfig::CONFIG['bindir'])
 RUBY_PATH = RUBY_BIN + RbConfig::CONFIG['ruby_install_name'] + RbConfig::CONFIG['EXEEXT']
 
-MACOS = true
 MACOS_FULL_VERSION = `/usr/bin/sw_vers -productVersion`.chomp
 MACOS_VERSION = ENV.fetch('MACOS_VERSION') { MACOS_FULL_VERSION[/10\.\d+/] }.to_f
 
diff --git a/Library/brew.rb b/Library/brew.rb
index 1ec1ad4c00..b72d61494f 100755
--- a/Library/brew.rb
+++ b/Library/brew.rb
@@ -35,7 +35,7 @@ case HOMEBREW_PREFIX.to_s when '/', '/usr'
   # it may work, but I only see pain this route and don't want to support it
   abort "Cowardly refusing to continue at this prefix: #{HOMEBREW_PREFIX}"
 end
-if MACOS and MACOS_VERSION < 10.5
+if OS.mac? and MacOS.version < 10.5
   abort <<-EOABORT.undent
     Homebrew requires Leopard or higher. For Tiger support, see:
     https://github.com/mistydemeo/tigerbrew