diff --git a/configure.ac b/configure.ac
index 15ccdd5..05c725f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1,6 +1,9 @@
 
 # Initialize Autoconf
-AC_PREREQ([2.70])
+# conda-forge patch: upstream nominally requires Autoconf 2.70, but our *current*
+# build framework only provides 2.69. The updated M2 epoch provides 2.71,
+# so we should upgrade to it! But the deps haven't been migrated yet.
+AC_PREREQ([2.69])
 AC_INIT([libX11], [1.8.9],
         [https://gitlab.freedesktop.org/xorg/lib/libx11/-/issues], [libX11])
 AC_CONFIG_SRCDIR([Makefile.am])