error: 'po/Makefile.in' is already registered with AC_CONFIG_FILES

[Narrat]

Trying to run the compile instructions nowadays lead to an error.

$ gettextize --no-changelog -f
Creating build-aux/ subdirectory
Copying file ABOUT-NLS
Copying file build-aux/config.rpath
Copying file po/Makefile.in.in
Copying file po/boldquot.sed
Copying file po/[email protected]
Copying file po/[email protected]
Copying file po/insert-header.sed
Copying file po/Makevars.template
Copying file po/quot.sed
Copying file po/remove-potcdate.sed
Copying file po/Rules-quot
Copying file m4/build-to-host.m4
Copying file m4/gettext.m4
Copying file m4/host-cpu-c-abi.m4
Copying file m4/iconv.m4
Copying file m4/intlmacosx.m4
Copying file m4/lib-ld.m4
Copying file m4/lib-link.m4
Copying file m4/lib-prefix.m4
Copying file m4/nls.m4
Copying file m4/po.m4
Copying file m4/progtest.m4
Updating configure.ac (backup is in configure.ac~)

Please run 'aclocal -I m4' to regenerate the aclocal.m4 file.
You need aclocal from GNU automake 1.9 (or newer) to do this.
Then run 'autoconf' to regenerate the configure file.

You will also need config.guess and config.sub, which you can get from the CVS
of the 'config' project at https://savannah.gnu.org/. The commands to fetch them
are
$ wget 'https://savannah.gnu.org/cgi-bin/viewcvs/*checkout*/config/config/config.guess'
$ wget 'https://savannah.gnu.org/cgi-bin/viewcvs/*checkout*/config/config/config.sub'

You might also want to copy the convenience header file gettext.h
from the /usr/share/gettext directory into your package.
It is a wrapper around <libintl.h> that implements the configure --disable-nls
option.

Press Return to acknowledge the previous three paragraphs.

$ autoconf
configure.ac:58: error: 'po/Makefile.in' is already registered with AC_CONFIG_FILES.
./lib/autoconf/status.m4:289: AC_CONFIG_FILES is expanded from...
configure.ac:58: the top level
autom4te: error: /usr/bin/m4 failed with exit status: 1

And indeed the configure.ac has the following change after running gettextize:

$  git diff configure.ac 
diff --git a/configure.ac b/configure.ac
index 7cd213b..0eb9e3a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -44,5 +44,5 @@ AC_CHECK_FUNCS([strdup strerror memset strchr strrchr strtoull], \
   [], [AC_MSG_ERROR([Function not found])])
 AC_CHECK_FUNCS([asprintf vasprintf])
 
-AC_OUTPUT([Makefile lib/Makefile src/Makefile man/Makefile po/Makefile.in])
+AC_OUTPUT([Makefile lib/Makefile src/Makefile man/Makefile po/Makefile.in po/Makefile.in])

Removing the duplicated entry allows to successfully run autoconf/autoreconf. But dunno where that comes from.