diff --git a/hawk/configure b/hawk/configure
index a6f2184e..ba3d132a 100755
--- a/hawk/configure
+++ b/hawk/configure
@@ -18517,6 +18517,59 @@ $as_echo "#define HAWK_PREFER_PREFIX_L 1" >>confdefs.h
 	fi
 fi
 
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for char16_t literal" >&5
+$as_echo_n "checking for char16_t literal... " >&6; }
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main ()
+{
+const void* x = u"ab cd ef gh";
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_link "$LINENO"; then :
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+$as_echo "yes" >&6; }
+
+$as_echo "#define HAWK_HAVE_PREFIX_SMALL_U 1" >>confdefs.h
+
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
+
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for char32_t literal" >&5
+$as_echo_n "checking for char32_t literal... " >&6; }
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main ()
+{
+const void* x = U"ab cd ef gh";
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_link "$LINENO"; then :
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+$as_echo "yes" >&6; }
+
+$as_echo "#define HAWK_HAVE_PREFIX_BIG_U 1" >>confdefs.h
+
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
 
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for __builtin_memset" >&5
 $as_echo_n "checking for __builtin_memset... " >&6; }
diff --git a/hawk/configure.ac b/hawk/configure.ac
index 06de6800..39829c81 100644
--- a/hawk/configure.ac
+++ b/hawk/configure.ac
@@ -169,6 +169,21 @@ else
 	fi
 fi
 
+AC_MSG_CHECKING([for char16_t literal])
+AC_LINK_IFELSE(
+	[AC_LANG_PROGRAM([], [const void* x = u"ab cd ef gh";])],
+	[AC_MSG_RESULT(yes)
+	 AC_DEFINE([HAWK_HAVE_PREFIX_SMALL_U], [1], [char16_t literal prefix])],
+	[AC_MSG_RESULT(no)]
+)
+
+AC_MSG_CHECKING([for char32_t literal])
+AC_LINK_IFELSE(
+	[AC_LANG_PROGRAM([], [const void* x = U"ab cd ef gh";])],
+	[AC_MSG_RESULT(yes)
+	 AC_DEFINE([HAWK_HAVE_PREFIX_BIG_U], [1], [char32_t literal prefix])],
+	[AC_MSG_RESULT(no)]
+)
 
 dnl check some compiler builtins
 AC_MSG_CHECKING([for __builtin_memset])
diff --git a/hawk/lib/hawk-cfg.h.in b/hawk/lib/hawk-cfg.h.in
index 6e85f22d..02eb803e 100644
--- a/hawk/lib/hawk-cfg.h.in
+++ b/hawk/lib/hawk-cfg.h.in
@@ -714,6 +714,12 @@
 /* Unknown Endian */
 #undef HAWK_ENDIAN_UNKNOWN
 
+/* char32_t literal prefix */
+#undef HAWK_HAVE_PREFIX_BIG_U
+
+/* char16_t literal prefix */
+#undef HAWK_HAVE_PREFIX_SMALL_U
+
 /* MB_LEN_MAX */
 #undef HAWK_MBLEN_MAX
 
diff --git a/hawk/lib/hawk-cmn.h b/hawk/lib/hawk-cmn.h
index b0a91cf0..11872893 100644
--- a/hawk/lib/hawk-cmn.h
+++ b/hawk/lib/hawk-cmn.h
@@ -510,7 +510,7 @@ typedef unsigned char           hawk_bchu_t; /* unsigned version of hawk_bch_t f
 	//   gcc/g++/clang/clang++: -fshort-wchar makes wchar_t to 2 bytes.
 	HAWK_STATIC_ASSERT (HAWK_WIDE_CHAR_SIZE == sizeof(hawk_uch_t));
 
-#elif defined(HAWK_WIDE_CHAR_SIZE) && (HAWK_WIDE_CHAR_SIZE >= 4) && defined(__GNUC__) && defined(__CHAR32_TYPE__)
+#elif defined(HAWK_WIDE_CHAR_SIZE) && (HAWK_WIDE_CHAR_SIZE >= 4) && defined(__GNUC__) && defined(__CHAR32_TYPE__) && defined(HAWK_HAVE_PREFIX_BIG_U)
 	typedef __CHAR32_TYPE__    hawk_uch_t;
 	typedef hawk_uint32_t      hawk_uchu_t;
 #	define HAWK_SIZEOF_UCH_T 4
@@ -523,7 +523,7 @@ typedef unsigned char           hawk_bchu_t; /* unsigned version of hawk_bch_t f
 	typedef hawk_uint32_t      hawk_uchu_t;
 #	define HAWK_SIZEOF_UCH_T 4
 
-#elif defined(__GNUC__) && defined(__CHAR16_TYPE__)
+#elif defined(__GNUC__) && defined(__CHAR16_TYPE__) && defined(HAWK_HAVE_PREFIX_SMALL_U)
 	typedef __CHAR16_TYPE__    hawk_uch_t;
 	typedef hawk_uint16_t      hawk_uchu_t;
 #	define HAWK_SIZEOF_UCH_T 2