diff --git a/config/c-library.m4 b/config/c-library.m4
index cddeafaec23..25bb5c69d15 100644
--- a/config/c-library.m4
+++ b/config/c-library.m4
@@ -325,4 +325,34 @@ fi
 if test "$pgac_cv_type_locale_t" = 'yes (in xlocale.h)'; then
   AC_DEFINE(LOCALE_T_IN_XLOCALE, 1,
             [Define to 1 if `locale_t' requires <xlocale.h>.])
-fi])])# PGAC_HEADER_XLOCALE
+fi])# PGAC_TYPE_LOCALE_T
+
+
+# PGAC_FUNC_WCSTOMBS_L
+# --------------------
+# Try to find a declaration for wcstombs_l().  It might be in stdlib.h
+# (following the POSIX requirement for wcstombs()), or in locale.h, or in
+# xlocale.h.  If it's in the latter, define WCSTOMBS_L_IN_XLOCALE.
+#
+AC_DEFUN([PGAC_FUNC_WCSTOMBS_L],
+[AC_CACHE_CHECK([for wcstombs_l declaration], pgac_cv_func_wcstombs_l,
+[AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
+[#include <stdlib.h>
+#include <locale.h>],
+[#ifndef wcstombs_l
+(void) wcstombs_l;
+#endif])],
+[pgac_cv_func_wcstombs_l='yes'],
+[AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
+[#include <stdlib.h>
+#include <locale.h>
+#include <xlocale.h>],
+[#ifndef wcstombs_l
+(void) wcstombs_l;
+#endif])],
+[pgac_cv_func_wcstombs_l='yes (in xlocale.h)'],
+[pgac_cv_func_wcstombs_l='no'])])])
+if test "$pgac_cv_func_wcstombs_l" = 'yes (in xlocale.h)'; then
+  AC_DEFINE(WCSTOMBS_L_IN_XLOCALE, 1,
+            [Define to 1 if `wcstombs_l' requires <xlocale.h>.])
+fi])# PGAC_FUNC_WCSTOMBS_L
diff --git a/configure b/configure
index 44a1c54fe8a..d12550629b6 100755
--- a/configure
+++ b/configure
@@ -19255,6 +19255,111 @@ _ACEOF
 fi
 
 
+{ $as_echo "$as_me:$LINENO: checking for wcstombs_l declaration" >&5
+$as_echo_n "checking for wcstombs_l declaration... " >&6; }
+if test "${pgac_cv_func_wcstombs_l+set}" = set; then
+  $as_echo_n "(cached) " >&6
+else
+  cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+#include <stdlib.h>
+#include <locale.h>
+int
+main ()
+{
+#ifndef wcstombs_l
+(void) wcstombs_l;
+#endif
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext
+if { (ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval ac_try_echo="\"\$as_me:$LINENO: $ac_try_echo\""
+$as_echo "$ac_try_echo") >&5
+  (eval "$ac_compile") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  $as_echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest.$ac_objext; then
+  pgac_cv_func_wcstombs_l='yes'
+else
+  $as_echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+#include <stdlib.h>
+#include <locale.h>
+#include <xlocale.h>
+int
+main ()
+{
+#ifndef wcstombs_l
+(void) wcstombs_l;
+#endif
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext
+if { (ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval ac_try_echo="\"\$as_me:$LINENO: $ac_try_echo\""
+$as_echo "$ac_try_echo") >&5
+  (eval "$ac_compile") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  $as_echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest.$ac_objext; then
+  pgac_cv_func_wcstombs_l='yes (in xlocale.h)'
+else
+  $as_echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	pgac_cv_func_wcstombs_l='no'
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
+{ $as_echo "$as_me:$LINENO: result: $pgac_cv_func_wcstombs_l" >&5
+$as_echo "$pgac_cv_func_wcstombs_l" >&6; }
+if test "$pgac_cv_func_wcstombs_l" = 'yes (in xlocale.h)'; then
+
+cat >>confdefs.h <<\_ACEOF
+#define WCSTOMBS_L_IN_XLOCALE 1
+_ACEOF
+
+fi
 
 # Some versions of libedit contain strlcpy(), setproctitle(), and other
 # symbols that that library has no business exposing to the world.  Pending
diff --git a/configure.in b/configure.in
index ec11d1847f3..e9b05869575 100644
--- a/configure.in
+++ b/configure.in
@@ -1235,6 +1235,7 @@ fi
 PGAC_VAR_INT_TIMEZONE
 AC_FUNC_ACCEPT_ARGTYPES
 PGAC_FUNC_GETTIMEOFDAY_1ARG
+PGAC_FUNC_WCSTOMBS_L
 
 # Some versions of libedit contain strlcpy(), setproctitle(), and other
 # symbols that that library has no business exposing to the world.  Pending
diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index 1843be9fd26..a25509c512f 100644
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -821,6 +821,9 @@
 /* Define to select Win32-style shared memory. */
 #undef USE_WIN32_SHARED_MEMORY
 
+/* Define to 1 if `wcstombs_l' requires <xlocale.h>. */
+#undef WCSTOMBS_L_IN_XLOCALE
+
 /* Define WORDS_BIGENDIAN to 1 if your processor stores words with the most
    significant byte first (like Motorola and SPARC, unlike Intel). */
 #if defined AC_APPLE_UNIVERSAL_BUILD
diff --git a/src/include/pg_config.h.win32 b/src/include/pg_config.h.win32
index 79ac65432fb..be6cae1f085 100644
--- a/src/include/pg_config.h.win32
+++ b/src/include/pg_config.h.win32
@@ -665,6 +665,9 @@
 /* Define to select Win32-style semaphores. */
 #define USE_WIN32_SEMAPHORES
 
+/* Define to 1 if `wcstombs_l' requires <xlocale.h>. */
+/* #undef WCSTOMBS_L_IN_XLOCALE */
+
 /* Number of bits in a file offset, on hosts where this is settable. */
 /* #undef _FILE_OFFSET_BITS */
 
diff --git a/src/include/utils/pg_locale.h b/src/include/utils/pg_locale.h
index c59a004fc9f..702168a9824 100644
--- a/src/include/utils/pg_locale.h
+++ b/src/include/utils/pg_locale.h
@@ -13,7 +13,7 @@
 #define _PG_LOCALE_
 
 #include <locale.h>
-#ifdef LOCALE_T_IN_XLOCALE
+#if defined(LOCALE_T_IN_XLOCALE) || defined(WCSTOMBS_L_IN_XLOCALE)
 #include <xlocale.h>
 #endif