--- a/lib/ChangeLog
+++ b/lib/ChangeLog
@@ -1,3 +1,8 @@
+2006-05-30  Ralf Wildenhues  <Ralf.Wildenhues@gmx.de>
+            Bruno Haible  <bruno@clisp.org>
+
+	* strndup.c (strndup) [!_LIBC]: Don't undefine macro definition.
+
 2006-05-26  Martin Lambers  <marlam@marlam.de>
 
 	* getpass.c: Updates the test for the native W32 API, and adds

--- a/lib/strndup.c
+++ b/lib/strndup.c
@@ -36,7 +36,9 @@
 #endif
 
 #undef __strndup
-#undef strndup
+#if _LIBC
+# undef strndup
+#endif
 
 #ifndef weak_alias
 # define __strndup strndup

--- a/m4/ChangeLog
+++ b/m4/ChangeLog
@@ -1,3 +1,11 @@
+2006-05-30  Ralf Wildenhues  <Ralf.Wildenhues@gmx.de>
+            Bruno Haible  <bruno@clisp.org>
+
+	* strndup.m4 (gl_FUNC_STRNDUP): Replace the AC_REPLACE_FUNCS with a
+	check for the declaration of strnlen and a run test that exposes the
+	AIX 5.1 strnlen bug.  In the failure case, #define strndup to
+	rpl_strndup.
+
 2006-05-28  Ralf Wildenhues  <Ralf.Wildenhues@gmx.de>
 
 	* c-strtod.m4 (gl_C99_STRTOLD): Use a link test rather than a

--- a/m4/strndup.m4
+++ b/m4/strndup.m4
@@ -1,5 +1,5 @@
-# strndup.m4 serial 5
-dnl Copyright (C) 2002, 2003, 2005 Free Software Foundation, Inc.
+# strndup.m4 serial 6
+dnl Copyright (C) 2002-2003, 2005-2006 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
 dnl with or without modifications, as long as this notice is preserved.
@@ -11,8 +11,36 @@
   dnl Persuade glibc <string.h> to declare strndup().
   AC_REQUIRE([AC_GNU_SOURCE])
 
-  AC_REPLACE_FUNCS(strndup)
-  if test $ac_cv_func_strndup = no; then
+  AC_CHECK_DECLS_ONCE([strndup])
+
+  # AIX 5.1 fails to add the terminating '\0'.
+  AC_CACHE_CHECK([for working strndup], gl_cv_func_strndup,
+    [AC_RUN_IFELSE([
+       AC_LANG_PROGRAM([#include <string.h>], [[
+#ifndef HAVE_DECL_STRNDUP
+  extern char *strndup (const char *, size_t);
+#endif
+  char *s;
+  s = strndup ("some longer string", 15);
+  free (s);
+  s = strndup ("shorter string", 13);
+  return s[13] != '\0';]])],
+       [gl_cv_func_strndup=yes],
+       [gl_cv_func_strndup=no],
+       [AC_EGREP_CPP([too risky], [
+#ifdef _AIX
+            too risky
+#endif
+          ],
+          [gl_cv_func_strndup=no],
+          [gl_cv_func_strndup=yes])])])
+  if test $gl_cv_func_strndup = yes; then
+    AC_DEFINE([HAVE_STRNDUP], 1,
+      [Define if you have the strndup() function and it works.])
+  else
+    AC_LIBOBJ([strndup])
+    AC_DEFINE(strndup, rpl_strndup,
+      [Define to rpl_strndup if the replacement function should be used,])
     gl_PREREQ_STRNDUP
   fi
 ])