diff --git a/cmd/principal/main_nacl.go b/cmd/principal/main_nacl.go
index 9dea3b5..e22d317 100644
--- a/cmd/principal/main_nacl.go
+++ b/cmd/principal/main_nacl.go
@@ -1,3 +1,7 @@
+// Copyright 2015 The Vanadium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
 package main
 
 const openCommand = ""