diff --git a/Library/Homebrew/cxxstdlib.rb b/Library/Homebrew/cxxstdlib.rb
index d04a86db0f..a7c84ac2da 100644
--- a/Library/Homebrew/cxxstdlib.rb
+++ b/Library/Homebrew/cxxstdlib.rb
@@ -1,7 +1,7 @@
 require "compilers"
 
 class CxxStdlib
-  attr_accessor :type, :compiler
+  attr_reader :type, :compiler
 
   def initialize(type, compiler)
     if type && ![:libstdcxx, :libcxx].include?(type)