diff --git a/metropolis/node/validation.go b/metropolis/node/validation.go
index cf6d520..982740c 100644
--- a/metropolis/node/validation.go
+++ b/metropolis/node/validation.go
@@ -1,3 +1,6 @@
+// Copyright The Monogon Project Authors.
+// SPDX-License-Identifier: Apache-2.0
+
 package node
 
 import (