diff --git a/tools/coverage.in b/tools/coverage.in
index 67dca02..eba9a4f 100644
--- a/tools/coverage.in
+++ b/tools/coverage.in
@@ -5,6 +5,11 @@
 ;;; Gash -- Guile As SHell
 ;;; Copyright © 2017 Timothy Sample <samplet@ngyro.com>
 ;;;
+;;; The 'coverage-data->lcov' procedure was adapted from:
+;;;
+;;; GNU Guile
+;;; Copyright (C) 2010, 2013, 2018 Free Software Foundation, Inc.
+;;;
 ;;; This file is part of Gash.
 ;;;
 ;;; Gash is free software: you can redistribute it and/or modify