diff --git a/doc/copyright.texi b/doc/copyright.texi
index 92b887801..509b94a09 100644
--- a/doc/copyright.texi
+++ b/doc/copyright.texi
@@ -59,6 +59,7 @@ SUCH DAMAGE.
 The parts of the libtelnet that handle Kerberos.
 
 @verbatim
+SPDX-License-Identifier: HPND-export-US
 
 Copyright (C) 1990 by the Massachusetts Institute of Technology