diff --git a/metropolis/proto/ext/gomod-generated-placeholder.go b/metropolis/proto/ext/gomod-generated-placeholder.go
index b39f0bb..5373719 100644
--- a/metropolis/proto/ext/gomod-generated-placeholder.go
+++ b/metropolis/proto/ext/gomod-generated-placeholder.go
@@ -1 +1,4 @@
+// Copyright The Monogon Project Authors.
+// SPDX-License-Identifier: Apache-2.0
+
 package ext