diff --git a/configure.ac b/configure.ac
index 560b4ac2..df99cfd4 100644
--- a/configure.ac
+++ b/configure.ac
@@ -30,6 +30,11 @@ dnl
 dnl Process this file with autoconf to produce a configure script.
 dnl
 
+dnl Error if AX_CODE_COVERAGE if missing (like on the 1.21 release).
+m4_pattern_forbid([^_?AX_])
+m4_pattern_allow([AX_CHECK_GNU_MAKE_HEADLINE])
+m4_pattern_allow([_AX_CODE_COVERAGE_GCOV_PROG_WITH])
+
 AC_INIT([wget],[m4_esyscmd(build-aux/git-version-gen .tarball-version)],[bug-wget@gnu.org])
 AC_PREREQ([2.64])