diff --git a/patches/pkgbuild/grep.sh b/patches/pkgbuild/grep.sh
index f1a0230..532612f 100755
--- a/patches/pkgbuild/grep.sh
+++ b/patches/pkgbuild/grep.sh
@@ -1,18 +1,36 @@
 #!/usr/bin/env bash
-# grep: skip ./bootstrap, which vets its host's autotools macros.
+# grep: neutralise the pkg.m4 serial check inside its own bootstrap script.
 #
 #   ./bootstrap: do not use pkg.m4 serial 12;
 #   see https://lists.gnu.org/r/grep-devel/2025-04/msg00006.html
 #
-# grep is the only package in this list that INSPECTS the version of the m4
-# macros its build host provides, and refuses to proceed on the serial Ubuntu
-# ships. It is not detecting a real incompatibility on s390x -- the same
+# grep is the only package here that INSPECTS the version of the m4 macros
+# its build host provides. This is not an s390x incompatibility: the same
 # refusal happens on any Ubuntu host, x86 included.
 #
-# The release tarball is already bootstrapped: configure, Makefile.in and the
-# gnulib tree are present. Re-running ./bootstrap regenerates what is already
-# there, so skipping it costs nothing.
+# A PREVIOUS VERSION of this hook skipped ./bootstrap entirely, on the
+# assumption that the source was a released tarball and therefore already
+# bootstrapped. It is not -- it is a git checkout, so skipping bootstrap
+# removed configure itself:
+#
+#   PKGBUILD: line 43: ./configure: No such file or directory
+#
+# The check itself is what has to go, and it lives in the extracted source,
+# so it is removed from prepare() rather than from the PKGBUILD directly.
 set -euo pipefail
-sed -i 's|^\(\s*\)\./bootstrap|\1# bootstrap skipped by the port: see patches/pkgbuild/grep.sh\n\1true|' PKGBUILD
-grep -qE '^\s*\./bootstrap' PKGBUILD && { echo "grep: bootstrap still invoked" >&2; exit 1; }
-echo "grep: ./bootstrap skipped (it rejects the host pkg.m4 serial)"
+python3 - <<'PY'
+import io, re
+s = io.open("PKGBUILD", encoding="utf-8").read()
+fix = """  # Port: drop bootstrap's host m4 vetting; see patches/pkgbuild/grep.sh
+  sed -i '/do not use pkg.m4 serial/,+1d' bootstrap
+"""
+m = re.search(r"\nprepare\(\) \{\n(\s*cd [^\n]*\n)", s)
+assert m, "prepare() with a cd not found"
+s = s[:m.end()] + fix + s[m.end():]
+io.open("PKGBUILD", "w", encoding="utf-8").write(s)
+PY
+grep -q "drop bootstrap's host m4 vetting" PKGBUILD || {
+    echo "grep: m4 check removal not inserted" >&2; exit 1; }
+grep -qE '^\s*\./bootstrap' PKGBUILD || {
+    echo "grep: bootstrap is no longer invoked -- configure would be missing" >&2; exit 1; }
+echo "grep: bootstrap kept, its pkg.m4 serial check neutralised"