diff --git a/LICENSE.txt b/LICENSE.txt
index 2ae74e3..36500ef 100644
--- a/LICENSE.txt
+++ b/LICENSE.txt
@@ -1,5 +1,7 @@
 The MIT License (MIT)
 
+Copyright (c) 2015 Preferred Infrastructure, Inc.
+Copyright (c) 2015 Preferred Networks, Inc.
 Copyright (c) 2017 yusaku.hatanaka
 
 Permission is hereby granted, free of charge, to any person obtaining a copy