diff --git a/sys-devel/m4/files/m4-1.4.19-fortify-source.patch b/sys-devel/m4/files/m4-1.4.19-fortify-source.patch
index 69e5405b6f2b0..d07fe620c3df0 100644
--- a/sys-devel/m4/files/m4-1.4.19-fortify-source.patch
+++ b/sys-devel/m4/files/m4-1.4.19-fortify-source.patch
@@ -1,3 +1,4 @@
+https://lists.gnu.org/archive/html/m4-patches/2023-01/msg00001.html
 https://bugs.gentoo.org/890273
 
 From 960b9b4d0774f78d286932251d6f53f638aefb19 Mon Sep 17 00:00:00 2001