diff -r 4e9fb4ce7cf9 configure.ac
--- a/configure.ac	Sat Dec 07 18:19:21 2013 +0100
+++ b/configure.ac	Sat Dec 07 22:46:35 2013 +0100
@@ -522,6 +522,13 @@
   AC_DEFINE(_POSIX_C_SOURCE, 200809L, Define to activate features from IEEE Stds 1003.1-2008)
 fi
 
+# On HP-UX mbstate_t requires _INCLUDE__STDC_A1_SOURCE
+case $ac_sys_system in
+hp*|HP*)
+  AC_DEFINE(_INCLUDE__STDC_A1_SOURCE, 1, Define to activate mbstate_t for mbrtowc)
+  ;;
+esac
+
 #
 # SGI compilers allow the specification of the both the ABI and the
 # ISA on the command line.  Depending on the values of these switches,