diff --git a/lib/em-dir-watcher.rb b/lib/em-dir-watcher.rb
index f82e7ad..0e87de8 100644
--- a/lib/em-dir-watcher.rb
+++ b/lib/em-dir-watcher.rb
@@ -4,7 +4,7 @@
 
 module EMDirWatcher
     PLATFORM = ENV['EM_DIR_WATCHER_PLATFORM'] ||
-        case Config::CONFIG['target_os']
+        case RbConfig::CONFIG['target_os']
             when /mswin|mingw/ then 'Windows'
             when /darwin/      then 'Mac'
             when /linux/       then 'Linux'