1 files changed, 1 insertions, 1 deletions
diff --git a/lib/singleton.rb b/lib/singleton.rb
index 2ee9b5b3b5..deb0f52cd6 100644
--- a/lib/singleton.rb
+++ b/lib/singleton.rb
@@ -133,7 +133,7 @@ module Singleton
     def __init__(klass) # :nodoc:
       klass.instance_eval {
         @singleton__instance__ = nil
-        @singleton__mutex__ = Mutex.new
+        @singleton__mutex__ = Thread::Mutex.new
       }
       def klass.instance # :nodoc:
         return @singleton__instance__ if @singleton__instance__