diff --git a/metropolis/proto/api/gomod-generated-placeholder.go b/metropolis/proto/api/gomod-generated-placeholder.go
index 778f64e..da08b30 100644
--- a/metropolis/proto/api/gomod-generated-placeholder.go
+++ b/metropolis/proto/api/gomod-generated-placeholder.go
@@ -1 +1,4 @@
+// Copyright The Monogon Project Authors.
+// SPDX-License-Identifier: Apache-2.0
+
 package api