diff --git a/metropolis/proto/private/gomod-generated-placeholder.go b/metropolis/proto/private/gomod-generated-placeholder.go
index 735e4dc..b4ed19a 100644
--- a/metropolis/proto/private/gomod-generated-placeholder.go
+++ b/metropolis/proto/private/gomod-generated-placeholder.go
@@ -1 +1,4 @@
+// Copyright The Monogon Project Authors.
+// SPDX-License-Identifier: Apache-2.0
+
 package private