diff --git a/lib/rb/ext/extconf.rb b/lib/rb/ext/extconf.rb
index 96f6b43..b35f60b 100644
--- a/lib/rb/ext/extconf.rb
+++ b/lib/rb/ext/extconf.rb
@@ -21,8 +21,10 @@
   File.open('Makefile', 'w'){|f| f.puts "all:\n\ninstall:\n" }
 else
   require 'mkmf'
+  require 'rbconfig'
 
-  $ARCH_FLAGS = Config::CONFIG['CFLAGS'].scan( /(-arch )(\S+)/ ).map{|x,y| x + y + ' ' }.join('')
+  $ARCH_FLAGS = RbConfig::CONFIG['CFLAGS'].scan( /(-arch )(\S+)/ ).map{|x,y| x + y + ' ' }.join('')
+
 
   $CFLAGS = "-fsigned-char -g -O2 -Wall -Werror " + $ARCH_FLAGS