diff --git a/module/system/base/pmatch.scm b/module/system/base/pmatch.scm
index 68ae5b28b..00563f689 100644
--- a/module/system/base/pmatch.scm
+++ b/module/system/base/pmatch.scm
@@ -1,4 +1,4 @@
-;;; pmatch
+;;; pmatch, a simple matcher
 
 ;;; Copyright (C) 2009, 2010 Free Software Foundation, Inc
 ;;; Copyright (C) 2005,2006,2007 Oleg Kiselyov
@@ -29,6 +29,9 @@
 ;;; Proceedings of the 2007 Workshop on Scheme and Functional Programming
 ;;; Université Laval Technical Report DIUL-RT-0701
 
+;;; To be clear: the original code is MIT-licensed, and the modifications
+;;; made to it by Guile are under Guile's license (currently LGPL v3+).
+
 ;;; Code:
 
 (define-module (system base pmatch)