--- a/m4/mbstate_t.m4
+++ b/m4/mbstate_t.m4
@@ -1,4 +1,4 @@
-# mbstate_t.m4 serial 10
+# mbstate_t.m4 serial 11
 dnl Copyright (C) 2000-2002, 2008 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -13,7 +13,10 @@
 # AC_TYPE_MBSTATE_T
 # -----------------
 AC_DEFUN([AC_TYPE_MBSTATE_T],
-  [AC_CACHE_CHECK([for mbstate_t], ac_cv_type_mbstate_t,
+[
+   AC_REQUIRE([AC_USE_SYSTEM_EXTENSIONS]) dnl for HP-UX 11.11
+
+   AC_CACHE_CHECK([for mbstate_t], ac_cv_type_mbstate_t,
      [AC_COMPILE_IFELSE(
 	[AC_LANG_PROGRAM(
 	   [AC_INCLUDES_DEFAULT[
@@ -27,4 +30,5 @@
    else
      AC_DEFINE([mbstate_t], int,
 	       [Define to a type if <wchar.h> does not define.])
-   fi])
+   fi
+])