diff --git a/src/runtime/mainthread/mainthread.go b/src/runtime/mainthread/mainthread.go
index b1267cb200d734..32fd70bc7bcc84 100644
--- a/src/runtime/mainthread/mainthread.go
+++ b/src/runtime/mainthread/mainthread.go
@@ -1,3 +1,7 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
 // Package mainthread mediates access to the program's main thread.
 //
 // Most Go programs do not need to run on specific threads