diff --git a/posix/bits/types.h b/posix/bits/types.h
index bd06e2d..5e22ce4 100644
--- a/posix/bits/types.h
+++ b/posix/bits/types.h
@@ -47,6 +47,16 @@ __extension__ typedef signed long long int __int64_t;
 __extension__ typedef unsigned long long int __uint64_t;
 #endif
 
+/* Smallest types with at least a given width.  */
+typedef __int8_t __int_least8_t;
+typedef __uint8_t __uint_least8_t;
+typedef __int16_t __int_least16_t;
+typedef __uint16_t __uint_least16_t;
+typedef __int32_t __int_least32_t;
+typedef __uint32_t __uint_least32_t;
+typedef __int64_t __int_least64_t;
+typedef __uint64_t __uint_least64_t;
+
 /* quad_t is also 64 bits.  */
 #if __WORDSIZE == 64
 typedef long int __quad_t;
diff --git a/sysdeps/generic/stdint.h b/sysdeps/generic/stdint.h
index 046d8bf..11fb0eb 100644
--- a/sysdeps/generic/stdint.h
+++ b/sysdeps/generic/stdint.h
@@ -40,26 +40,16 @@
 /* Small types.  */
 
 /* Signed.  */
-typedef signed char		int_least8_t;
-typedef short int		int_least16_t;
-typedef int			int_least32_t;
-#if __WORDSIZE == 64
-typedef long int		int_least64_t;
-#else
-__extension__
-typedef long long int		int_least64_t;
-#endif
+typedef __int_least8_t int_least8_t;
+typedef __int_least16_t int_least16_t;
+typedef __int_least32_t int_least32_t;
+typedef __int_least64_t int_least64_t;
 
 /* Unsigned.  */
-typedef unsigned char		uint_least8_t;
-typedef unsigned short int	uint_least16_t;
-typedef unsigned int		uint_least32_t;
-#if __WORDSIZE == 64
-typedef unsigned long int	uint_least64_t;
-#else
-__extension__
-typedef unsigned long long int	uint_least64_t;
-#endif
+typedef __uint_least8_t uint_least8_t;
+typedef __uint_least16_t uint_least16_t;
+typedef __uint_least32_t uint_least32_t;
+typedef __uint_least64_t uint_least64_t;
 
 
 /* Fast types.  */
diff --git a/wcsmbs/Makefile b/wcsmbs/Makefile
index 653e289..3ee91d2 100644
--- a/wcsmbs/Makefile
+++ b/wcsmbs/Makefile
@@ -50,7 +50,7 @@ strop-tests :=  wcscmp wcsncmp wmemcmp wcslen wcschr wcsrchr wcscpy wcsnlen \
 tests := tst-wcstof wcsmbs-tst1 tst-wcsnlen tst-btowc tst-mbrtowc \
 	 tst-wcrtomb tst-wcpncpy tst-mbsrtowcs tst-wchar-h tst-mbrtowc2 \
 	 tst-c16c32-1 wcsatcliff tst-wcstol-locale tst-wcstod-nan-locale \
-	 tst-wcstod-round \
+	 tst-wcstod-round test-char-types \
 	 $(addprefix test-,$(strop-tests))
 
 include ../Rules
diff --git a/wcsmbs/test-char-types.c b/wcsmbs/test-char-types.c
new file mode 100644
index 0000000..3123761
--- /dev/null
+++ b/wcsmbs/test-char-types.c
@@ -0,0 +1,31 @@
+/* Test char16_t and char32_t types consistent with compiler.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <uchar.h>
+
+const char16_t *s16 = u"";
+const char32_t *s32 = U"";
+
+static int
+do_test (void)
+{
+  /* This is a compilation test.  */
+  return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/wcsmbs/uchar.h b/wcsmbs/uchar.h
index 4d78f70..4d9b2ec 100644
--- a/wcsmbs/uchar.h
+++ b/wcsmbs/uchar.h
@@ -28,20 +28,13 @@
 #define __need_size_t
 #include <stddef.h>
 
+#include <bits/types.h>
 #include <bits/types/mbstate_t.h>
 
-#if defined __GNUC__ && !defined __USE_ISOCXX11
-/* Define the 16-bit and 32-bit character types.  Use the information
-   provided by the compiler.  */
-# if !defined __CHAR16_TYPE__ || !defined __CHAR32_TYPE__
-#  if defined __STDC_VERSION__ && __STDC_VERSION__ < 201000L
-#   error "<uchar.h> requires ISO C11 mode"
-#  else
-#   error "definitions of __CHAR16_TYPE__ and/or __CHAR32_TYPE__ missing"
-#  endif
-# endif
-typedef __CHAR16_TYPE__ char16_t;
-typedef __CHAR32_TYPE__ char32_t;
+#ifndef __USE_ISOCXX11
+/* Define the 16-bit and 32-bit character types.  */
+typedef __uint_least16_t char16_t;
+typedef __uint_least32_t char32_t;
 #endif
 
 
