diff --git a/Library/Homebrew/macos.rb b/Library/Homebrew/macos.rb
index cf80d1dd6f..dd88e122b2 100644
--- a/Library/Homebrew/macos.rb
+++ b/Library/Homebrew/macos.rb
@@ -75,7 +75,7 @@ module MacOS extend self
       opts << "#{Xcode.prefix}/Platforms/MacOSX.platform/Developer/SDKs/MacOSX#{v}.sdk"
       # Xcode < 4.3 style
       opts << "/Developer/SDKs/MacOS#{v}.sdk"
-      opts.map{|a| Pathname.new(a) }.detect(&:directory?)
+      opts.map{|a| Pathname.new(a) }.detect { |p| p.directory? }
     end
   end