--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2010-08-28  Bruno Haible  <bruno@clisp.org>
+
+	Prefer using AC_DEFUN_ONCE over AC_DEFUN in projects with gnulib.
+	* m4/iconv.m4 (gl_iconv_AC_DEFUN): Use AC_DEFUN_ONCE if gl_00GNULIB is
+	defined.
+	* m4/libunistring.m4 (gl_libunistring_AC_DEFUN): Likewise.
+	Suggested by Eric Blake.
+
 2010-08-28  Bruno Haible  <bruno@clisp.org>
 
 	sys_socket, netdb: Ensure socklen_t gets defined.

--- a/m4/iconv.m4
+++ b/m4/iconv.m4
@@ -1,4 +1,4 @@
-# iconv.m4 serial 14 (gettext-0.18.2)
+# iconv.m4 serial 15 (gettext-0.18.2)
 dnl Copyright (C) 2000-2002, 2007-2010 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -217,8 +217,11 @@
   m4_version_prereq([2.64],
     [[AC_DEFUN_ONCE(
         [$1], [$2])]],
-    [[AC_DEFUN(
-        [$1], [$2])]]))
+    [m4_ifdef([gl_00GNULIB],
+       [[AC_DEFUN_ONCE(
+           [$1], [$2])]],
+       [[AC_DEFUN(
+           [$1], [$2])]])]))
 gl_iconv_AC_DEFUN([AM_ICONV],
 [
   AM_ICONV_LINK

--- a/m4/libunistring.m4
+++ b/m4/libunistring.m4
@@ -1,4 +1,4 @@
-# libunistring.m4 serial 10
+# libunistring.m4 serial 11
 dnl Copyright (C) 2009-2010 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -25,8 +25,11 @@
   m4_version_prereq([2.64],
     [[AC_DEFUN_ONCE(
         [$1], [$2])]],
-    [[AC_DEFUN(
-        [$1], [$2])]]))
+    [m4_ifdef([gl_00GNULIB],
+       [[AC_DEFUN_ONCE(
+           [$1], [$2])]],
+       [[AC_DEFUN(
+           [$1], [$2])]])]))
 gl_libunistring_AC_DEFUN([gl_LIBUNISTRING],
 [
   AC_BEFORE([$0], [gl_LIBUNISTRING_MODULE])