diff --git a/gen-toc-based-on-docbook5.py b/gen-toc-based-on-docbook5.py
index b46c4fe..ae07500 100644
--- a/gen-toc-based-on-docbook5.py
+++ b/gen-toc-based-on-docbook5.py
@@ -5,6 +5,11 @@
 # Copyright © 2019 Shlomi Fish <shlomif@cpan.org>
 #
 # Distributed under terms of the MIT license.
+#
+# Based in part on "topic.py" ,(c) Xavier Combelle here made in public domain
+# ( https://github.com/shlomif/Freenode-programming-channel-FAQ/blob/
+#   b171f5367a5f54a430c4f727c757106107793e59/topic.py )
+# ( https://is.gd/7TJun3 )
 
 import re
 
diff --git a/topic.py b/topic.py
index 6d5ced2..5fc2093 100644
--- a/topic.py
+++ b/topic.py
@@ -1,6 +1,9 @@
 #!/usr/bin/env python3
 # (c) Xavier Combelle here made in public domain
 
+# NOTE: we now use gen-toc-based-on-docbook5.py instead, but this program
+# may have other use-cases.
+
 import argparse
 import subprocess
 import sys