diff --git a/metropolis/test/swtpm/certtool/main.go b/metropolis/test/swtpm/certtool/main.go
index 5079c54..600d9aa 100644
--- a/metropolis/test/swtpm/certtool/main.go
+++ b/metropolis/test/swtpm/certtool/main.go
@@ -1,3 +1,6 @@
+// Copyright The Monogon Project Authors.
+// SPDX-License-Identifier: Apache-2.0
+
 package main
 
 // Minimal GnuTLS certtool-like tool in Go. Implements only what's needed for