diff --git a/lib/mail_catcher.rb b/lib/mail_catcher.rb
index eac943e..ca19f02 100644
--- a/lib/mail_catcher.rb
+++ b/lib/mail_catcher.rb
@@ -16,11 +16,11 @@ module MailCatcher
 module_function
 
   def mac?
-    Config::CONFIG['host_os'] =~ /darwin/
+    RbConfig::CONFIG['host_os'] =~ /darwin/
   end
 
   def windows?
-    Config::CONFIG['host_os'] =~ /mswin|mingw/
+    RbConfig::CONFIG['host_os'] =~ /mswin|mingw/
   end
 
   def macruby?