diff --git a/Library/Homebrew/extend/ENV.rb b/Library/Homebrew/extend/ENV.rb
index ff51ced66b..3cba7719c8 100644
--- a/Library/Homebrew/extend/ENV.rb
+++ b/Library/Homebrew/extend/ENV.rb
@@ -201,6 +201,7 @@ module HomebrewEnvExtension
   end
 
   def macosxsdk v=MacOS.version
+    return unless MACOS
     # Sets all needed lib and include dirs to CFLAGS, CPPFLAGS, LDFLAGS.
     remove_macosxsdk
     # Allow cool style of ENV.macosxsdk 10.8 here (no "" :)
diff --git a/Library/Homebrew/keg_fix_install_names.rb b/Library/Homebrew/keg_fix_install_names.rb
index 34669da3ca..dd647660a5 100644
--- a/Library/Homebrew/keg_fix_install_names.rb
+++ b/Library/Homebrew/keg_fix_install_names.rb
@@ -1,5 +1,6 @@
 class Keg
   def fix_install_names
+    return unless MACOS
     mach_o_files.each do |file|
       bad_install_names_for file do |id, bad_names|
         file.ensure_writable do
diff --git a/Library/Homebrew/macos.rb b/Library/Homebrew/macos.rb
index dae0a1126a..b28be62dc4 100644
--- a/Library/Homebrew/macos.rb
+++ b/Library/Homebrew/macos.rb
@@ -227,6 +227,7 @@ module MacOS extend self
   end
 
   def mdfind id
+    return [] unless MACOS
     (@mdfind ||= {}).fetch(id.to_s) do
       @mdfind[id.to_s] = `/usr/bin/mdfind "kMDItemCFBundleIdentifier == '#{id}'"`.split("\n")
     end