diff --git a/buildsys.mk.in b/buildsys.mk.in
index 35432ad..f9495ac 100644
--- a/buildsys.mk.in
+++ b/buildsys.mk.in
@@ -1,6 +1,8 @@
 #
 #  Copyright (c) 2007, Jonathan Schleifer <js-buildsys@webkeks.org>
 #
+#  https://webkeks.org/hg/buildsys/
+#
 #  Permission to use, copy, modify, and/or distribute this software for any
 #  purpose with or without fee is hereby granted, provided that the above
 #  copyright notice and this permission notice is present in all copies.
diff --git a/m4/buildsys.m4 b/m4/buildsys.m4
index 3b1545f..4520e42 100644
--- a/m4/buildsys.m4
+++ b/m4/buildsys.m4
@@ -1,6 +1,8 @@
 dnl
 dnl Copyright (c) 2007, Jonathan Schleifer <js-buildsys@webkeks.org>
 dnl
+dnl https://webkeks.org/hg/buildsys/
+dnl
 dnl Permission to use, copy, modify, and/or distribute this software for any
 dnl purpose with or without fee is hereby granted, provided that the above
 dnl copyright notice and this permission notice is present in all copies.