diff --git a/stdio-common/Makefile b/stdio-common/Makefile
index 63c9ebd..309d83e 100644
--- a/stdio-common/Makefile
+++ b/stdio-common/Makefile
@@ -60,6 +60,7 @@ tests := tstscanf test_rdwr test-popen tstgetln test-fseek \
 	 bug25 tst-printf-round bug23-2 bug23-3 bug23-4 bug26 tst-fmemopen3 \
 	 tst-printf-bz18872 tst-vfprintf-width-prec tst-fmemopen4 \
 	 tst-vfprintf-user-type \
+	 tst-vfprintf-mbs-prec \
 
 test-srcs = tst-unbputc tst-printf
 
diff --git a/stdio-common/tst-vfprintf-mbs-prec.c b/stdio-common/tst-vfprintf-mbs-prec.c
new file mode 100644
index 0000000..43e4519
--- /dev/null
+++ b/stdio-common/tst-vfprintf-mbs-prec.c
@@ -0,0 +1,543 @@
+/* Test for wchar_t/multi-byte conversion and precision in vfprintf.
+   Copyright (C) 2017 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 <locale.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+#include <support/check.h>
+#include <support/test-driver.h>
+#include <wchar.h>
+
+#define DYNARRAY_STRUCT str
+#define DYNARRAY_ELEMENT char
+#define DYNARRAY_PREFIX str_
+#include <malloc/dynarray-skeleton.c>
+
+#define DYNARRAY_STRUCT wstr
+#define DYNARRAY_ELEMENT wchar_t
+#define DYNARRAY_PREFIX wstr_
+#include <malloc/dynarray-skeleton.c>
+
+#define DYNARRAY_STRUCT len
+#define DYNARRAY_ELEMENT size_t
+#define DYNARRAY_PREFIX len_
+#include <malloc/dynarray-skeleton.c>
+
+/* This should be larger than the internal buffer in vfprintf.  The
+   constant needs to be kept in sync with the format strings in
+   test_mbs_long and test_wide_long.  */
+enum { WIDE_STRING_LENGTH = 1000 };
+
+/* Creates two large, random strings used for truncation testing.
+   After the call, *MBS will be encoded in UTF-8, and *WIDE will
+   contain the same string in the internal UCS-32 encoding.  Both
+   strings are null-terminated.  The array *LENGTH counts the number
+   of multi-byte characters for each prefix string of *WIDE: The first
+   N wide characters of *WIDE correspond the first (*LENGTH)[N] bytes
+   of *MBS.  The caller should deallocate all three arrays using
+   free.  */
+static void
+make_random_string (char **mbs, wchar_t **wide, size_t **length)
+{
+  struct str str;
+  str_init (&str);
+  struct wstr wstr;
+  wstr_init (&wstr);
+  struct len len;
+  len_init (&len);
+
+  for (int i = 0; i < WIDE_STRING_LENGTH; ++i)
+    {
+      len_add (&len, str_size (&str));
+      /* Cover some multi-byte UTF-8 sequences.  Avoid the null
+         character.  */
+      uint32_t ch = 1 + (rand () % 521);
+      wstr_add (&wstr, ch);
+
+      /* Limited UTF-8 conversion.  */
+      if (ch <= 127)
+        str_add (&str, ch);
+      else
+        {
+          /* We only implement two-byte sequences.  */
+          uint32_t first = ch >> 6;
+          TEST_VERIFY (first < 32);
+          str_add (&str, 0xC0 | first);
+          str_add (&str, 0x80 | (ch & 0x3f));
+        }
+    }
+  len_add (&len, str_size (&str));
+  wstr_add (&wstr, L'\0');
+  str_add (&str, '\0');
+
+  *mbs = str_finalize (&str, NULL);
+  TEST_VERIFY_EXIT (*mbs != NULL);
+  *wide = wstr_finalize (&wstr, NULL);
+  TEST_VERIFY_EXIT (*wide != NULL);
+  *length = len_finalize (&len, NULL);
+  TEST_VERIFY_EXIT (*length != NULL);
+}
+
+/* snprintf tests (multi-byte result).  */
+static void
+test_mbs_result (void)
+{
+  char buf[200];
+
+  /* ASCII wide string.  */
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%ls", L"xyz") == 3);
+  TEST_VERIFY (strcmp (buf, "xyz") == 0);
+
+  /* Unicode wide string.  */
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%ls", L"x\u00DFz") == 4);
+  TEST_VERIFY (strcmp (buf, "x\xC3\x9Fz") == 0);
+
+  /* Varying precisions.  */
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%.1ls", L"x\u00DFz") == 1);
+  TEST_VERIFY (strcmp (buf, "x") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%.2ls", L"x\u00DFz") == 1);
+  TEST_VERIFY (strcmp (buf, "x") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%.3ls", L"x\u00DFz") == 3);
+  TEST_VERIFY (strcmp (buf, "x\xC3\x9F") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%.4ls", L"x\u00DFz") == 4);
+  TEST_VERIFY (strcmp (buf, "x\xC3\x9Fz") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%.5ls", L"x\u00DFz") == 4);
+  TEST_VERIFY (strcmp (buf, "x\xC3\x9Fz") == 0);
+
+  /* Varying precisions with width 2, right-justified.  */
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%2.1ls", L"x\u00DFz") == 2);
+  TEST_VERIFY (strcmp (buf, " x") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%2.2ls", L"x\u00DFz") == 2);
+  TEST_VERIFY (strcmp (buf, " x") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%2.3ls", L"x\u00DFz") == 3);
+  TEST_VERIFY (strcmp (buf, "x\xC3\x9F") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%2.4ls", L"x\u00DFz") == 4);
+  TEST_VERIFY (strcmp (buf, "x\xC3\x9Fz") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%2.5ls", L"x\u00DFz") == 4);
+  TEST_VERIFY (strcmp (buf, "x\xC3\x9Fz") == 0);
+
+  /* Varying precisions with width 2, left-justified.  */
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%-2.1ls", L"x\u00DFz") == 2);
+  TEST_VERIFY (strcmp (buf, "x ") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%-2.2ls", L"x\u00DFz") == 2);
+  TEST_VERIFY (strcmp (buf, "x ") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%-2.3ls", L"x\u00DFz") == 3);
+  TEST_VERIFY (strcmp (buf, "x\xC3\x9F") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%-2.4ls", L"x\u00DFz") == 4);
+  TEST_VERIFY (strcmp (buf, "x\xC3\x9Fz") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%-2.5ls", L"x\u00DFz") == 4);
+  TEST_VERIFY (strcmp (buf, "x\xC3\x9Fz") == 0);
+
+  /* Varying precisions with width 3, right-justified.  */
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%3.1ls", L"x\u00DFz") == 3);
+  TEST_VERIFY (strcmp (buf, "  x") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%3.2ls", L"x\u00DFz") == 3);
+  TEST_VERIFY (strcmp (buf, "  x") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%3.3ls", L"x\u00DFz") == 3);
+  TEST_VERIFY (strcmp (buf, "x\xC3\x9F") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%3.4ls", L"x\u00DFz") == 4);
+  TEST_VERIFY (strcmp (buf, "x\xC3\x9Fz") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%3.5ls", L"x\u00DFz") == 4);
+  TEST_VERIFY (strcmp (buf, "x\xC3\x9Fz") == 0);
+
+  /* Varying precisions with width 3, left-justified.  */
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%-3.1ls", L"x\u00DFz") == 3);
+  TEST_VERIFY (strcmp (buf, "x  ") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%-3.2ls", L"x\u00DFz") == 3);
+  TEST_VERIFY (strcmp (buf, "x  ") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%-3.3ls", L"x\u00DFz") == 3);
+  TEST_VERIFY (strcmp (buf, "x\xC3\x9F") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%-3.4ls", L"x\u00DFz") == 4);
+  TEST_VERIFY (strcmp (buf, "x\xC3\x9Fz") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%-3.5ls", L"x\u00DFz") == 4);
+  TEST_VERIFY (strcmp (buf, "x\xC3\x9Fz") == 0);
+
+  /* Varying precisions with width 4, right-justified.  */
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%4.1ls", L"x\u00DFz") == 4);
+  TEST_VERIFY (strcmp (buf, "   x") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%4.2ls", L"x\u00DFz") == 4);
+  TEST_VERIFY (strcmp (buf, "   x") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%4.3ls", L"x\u00DFz") == 4);
+  TEST_VERIFY (strcmp (buf, " x\xC3\x9F") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%4.4ls", L"x\u00DFz") == 4);
+  TEST_VERIFY (strcmp (buf, "x\xC3\x9Fz") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%4.5ls", L"x\u00DFz") == 4);
+  TEST_VERIFY (strcmp (buf, "x\xC3\x9Fz") == 0);
+
+  /* Varying precisions with width 4, left-justified.  */
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%-4.1ls", L"x\u00DFz") == 4);
+  TEST_VERIFY (strcmp (buf, "x   ") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%-4.2ls", L"x\u00DFz") == 4);
+  TEST_VERIFY (strcmp (buf, "x   ") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%-4.3ls", L"x\u00DFz") == 4);
+  TEST_VERIFY (strcmp (buf, "x\xC3\x9F ") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%-4.4ls", L"x\u00DFz") == 4);
+  TEST_VERIFY (strcmp (buf, "x\xC3\x9Fz") == 0);
+  memset (buf, '@', sizeof (buf));
+  TEST_VERIFY (snprintf (buf, sizeof (buf), "%-4.5ls", L"x\u00DFz") == 4);
+  TEST_VERIFY (strcmp (buf, "x\xC3\x9Fz") == 0);
+}
+
+/* swprintf tests (wide string result).  */
+static void
+test_wide_result (void)
+{
+  enum { size = 20 };
+  wchar_t buf[20];
+
+  /* ASCII wide string.  */
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%s", "xyz") == 3);
+  TEST_VERIFY (wcscmp (buf, L"xyz") == 0);
+
+  /* Unicode wide string.  */
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%s", "x\xC3\x9Fz") == 3);
+  TEST_VERIFY (wcscmp (buf, L"x\u00DFz") == 0);
+
+  /* Varying precisions.  */
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%.1s", "x\xC3\x9Fz") == 1);
+  TEST_VERIFY (wcscmp (buf, L"x") == 0);
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%.2s", "x\xC3\x9Fz") == 2);
+  TEST_VERIFY (wcscmp (buf, L"x\u00DF") == 0);
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%.3s", "x\xC3\x9Fz") == 3);
+  TEST_VERIFY (wcscmp (buf, L"x\u00DFz") == 0);
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%.4s", "x\xC3\x9Fz") == 3);
+  TEST_VERIFY (wcscmp (buf, L"x\u00DFz") == 0);
+
+  /* Varying precisions with width 2, right-justified.  */
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%2.1s", "x\xC3\x9Fz") == 2);
+  TEST_VERIFY (wcscmp (buf, L" x") == 0);
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%2.2s", "x\xC3\x9Fz") == 2);
+  TEST_VERIFY (wcscmp (buf, L"x\u00DF") == 0);
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%2.3s", "x\xC3\x9Fz") == 3);
+  TEST_VERIFY (wcscmp (buf, L"x\u00DFz") == 0);
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%2.4s", "x\xC3\x9Fz") == 3);
+  TEST_VERIFY (wcscmp (buf, L"x\u00DFz") == 0);
+
+  /* Varying precisions with width 2, left-justified.  */
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%-2.1s", "x\xC3\x9Fz") == 2);
+  TEST_VERIFY (wcscmp (buf, L"x ") == 0);
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%-2.2s", "x\xC3\x9Fz") == 2);
+  TEST_VERIFY (wcscmp (buf, L"x\u00DF") == 0);
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%-2.3s", "x\xC3\x9Fz") == 3);
+  TEST_VERIFY (wcscmp (buf, L"x\u00DFz") == 0);
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%-2.4s", "x\xC3\x9Fz") == 3);
+  TEST_VERIFY (wcscmp (buf, L"x\u00DFz") == 0);
+
+  /* Varying precisions with width 3, right-justified.  */
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%3.1s", "x\xC3\x9Fz") == 3);
+  TEST_VERIFY (wcscmp (buf, L"  x") == 0);
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%3.2s", "x\xC3\x9Fz") == 3);
+  TEST_VERIFY (wcscmp (buf, L" x\u00DF") == 0);
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%3.3s", "x\xC3\x9Fz") == 3);
+  TEST_VERIFY (wcscmp (buf, L"x\u00DFz") == 0);
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%3.4s", "x\xC3\x9Fz") == 3);
+  TEST_VERIFY (wcscmp (buf, L"x\u00DFz") == 0);
+
+  /* Varying precisions with width 3, left-justified.  */
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%-3.1s", "x\xC3\x9Fz") == 3);
+  TEST_VERIFY (wcscmp (buf, L"x  ") == 0);
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%-3.2s", "x\xC3\x9Fz") == 3);
+  TEST_VERIFY (wcscmp (buf, L"x\u00DF ") == 0);
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%-3.3s", "x\xC3\x9Fz") == 3);
+  TEST_VERIFY (wcscmp (buf, L"x\u00DFz") == 0);
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%-3.4s", "x\xC3\x9Fz") == 3);
+  TEST_VERIFY (wcscmp (buf, L"x\u00DFz") == 0);
+
+  /* Varying precisions with width 4, right-justified.  */
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%4.1s", "x\xC3\x9Fz") == 4);
+  TEST_VERIFY (wcscmp (buf, L"   x") == 0);
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%4.2s", "x\xC3\x9Fz") == 4);
+  TEST_VERIFY (wcscmp (buf, L"  x\u00DF") == 0);
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%4.3s", "x\xC3\x9Fz") == 4);
+  TEST_VERIFY (wcscmp (buf, L" x\u00DFz") == 0);
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%4.4s", "x\xC3\x9Fz") == 4);
+  TEST_VERIFY (wcscmp (buf, L" x\u00DFz") == 0);
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%4.5s", "x\xC3\x9Fz") == 4);
+  TEST_VERIFY (wcscmp (buf, L" x\u00DFz") == 0);
+
+  /* Varying precisions with width 4, left-justified.  */
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%-4.1s", "x\xC3\x9Fz") == 4);
+  TEST_VERIFY (wcscmp (buf, L"x   ") == 0);
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%-4.2s", "x\xC3\x9Fz") == 4);
+  TEST_VERIFY (wcscmp (buf, L"x\u00DF  ") == 0);
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%-4.3s", "x\xC3\x9Fz") == 4);
+  TEST_VERIFY (wcscmp (buf, L"x\u00DFz ") == 0);
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%-4.4s", "x\xC3\x9Fz") == 4);
+  TEST_VERIFY (wcscmp (buf, L"x\u00DFz ") == 0);
+  wmemset (buf, '@', size);
+  TEST_VERIFY (swprintf (buf, size, L"%-4.5s", "x\xC3\x9Fz") == 4);
+  TEST_VERIFY (wcscmp (buf, L"x\u00DFz ") == 0);
+}
+
+/* Test with long strings and multi-byte result.  */
+static void
+test_mbs_long (const char *mbs, const wchar_t *wide, const size_t *length)
+{
+  char buf[4000];
+  _Static_assert (sizeof (buf) > 3 * WIDE_STRING_LENGTH,
+                  "buffer size consistent with string length");
+  const char *suffix = "||TERM";
+  TEST_VERIFY_EXIT (sizeof (buf)
+                    > length[WIDE_STRING_LENGTH] + strlen (suffix));
+
+  /* Test formatting of the entire string.  */
+  {
+    int ret = snprintf (buf, sizeof (buf), "%ls%s", wide, suffix);
+    TEST_VERIFY (ret == length[WIDE_STRING_LENGTH] + strlen (suffix));
+    TEST_VERIFY (memcmp (buf, mbs, length[WIDE_STRING_LENGTH]) == 0);
+    TEST_VERIFY (strcmp (buf + length[WIDE_STRING_LENGTH], suffix) == 0);
+
+    /* Left-justified string, printed in full.  */
+    ret = snprintf (buf, sizeof (buf), "%-3500ls%s", wide, suffix);
+    TEST_VERIFY (ret == 3500 + strlen (suffix));
+    TEST_VERIFY (memcmp (buf, mbs, length[WIDE_STRING_LENGTH]) == 0);
+    for (size_t i = length[WIDE_STRING_LENGTH]; i < 3500; ++i)
+      TEST_VERIFY (buf[i] == ' ');
+    TEST_VERIFY (strcmp (buf + 3500, suffix) == 0);
+
+    /* Right-justified string, printed in full.   */
+    ret = snprintf (buf, sizeof (buf), "%3500ls%s", wide, suffix);
+    TEST_VERIFY (ret == 3500 + strlen (suffix));
+    size_t padding = 3500 - length[WIDE_STRING_LENGTH];
+    for (size_t i = 0; i < padding; ++i)
+      TEST_VERIFY (buf[i] == ' ');
+    TEST_VERIFY (memcmp (buf + padding, mbs, length[WIDE_STRING_LENGTH]) == 0);
+    TEST_VERIFY (strcmp (buf + 3500, suffix) == 0);
+  }
+
+  size_t wide_characters_converted = 0;
+  for (int mbs_len = 0; mbs_len <= length[WIDE_STRING_LENGTH] + 1;
+       ++mbs_len)
+    {
+      if (wide_characters_converted < WIDE_STRING_LENGTH
+          && mbs_len >= length[wide_characters_converted + 1])
+        /* The requested prefix length contains room for another wide
+           character.  */
+        ++wide_characters_converted;
+      if (test_verbose > 0)
+        printf ("info: %s: mbs_len=%d wide_chars_converted=%zu length=%zu\n",
+                __func__, mbs_len, wide_characters_converted,
+                length[wide_characters_converted]);
+      TEST_VERIFY (length[wide_characters_converted] <= mbs_len);
+      TEST_VERIFY (wide_characters_converted == 0
+                   || length[wide_characters_converted - 1] < mbs_len);
+
+      int ret = snprintf (buf, sizeof (buf), "%.*ls%s", mbs_len, wide, suffix);
+      TEST_VERIFY (ret == length[wide_characters_converted] + strlen (suffix));
+      TEST_VERIFY (memcmp (buf, mbs, length[wide_characters_converted]) == 0);
+      TEST_VERIFY (strcmp (buf + length[wide_characters_converted],
+                           suffix) == 0);
+
+      /* Left-justified string, printed in full.  */
+      if (test_verbose)
+        printf ("info: %s: left-justified\n", __func__);
+      ret = snprintf (buf, sizeof (buf), "%-3500.*ls%s",
+                      mbs_len, wide, suffix);
+      TEST_VERIFY (ret == 3500 + strlen (suffix));
+      TEST_VERIFY (memcmp (buf, mbs, length[wide_characters_converted]) == 0);
+      for (size_t i = length[wide_characters_converted]; i < 3500; ++i)
+        TEST_VERIFY (buf[i] == ' ');
+      TEST_VERIFY (strcmp (buf + 3500, suffix) == 0);
+
+      /* Right-justified string, printed in full.   */
+      if (test_verbose)
+        printf ("info: %s: right-justified\n", __func__);
+      ret = snprintf (buf, sizeof (buf), "%3500.*ls%s", mbs_len, wide, suffix);
+      TEST_VERIFY (ret == 3500 + strlen (suffix));
+      size_t padding = 3500 - length[wide_characters_converted];
+      for (size_t i = 0; i < padding; ++i)
+        TEST_VERIFY (buf[i] == ' ');
+      TEST_VERIFY (memcmp (buf + padding, mbs,
+                           length[wide_characters_converted]) == 0);
+      TEST_VERIFY (strcmp (buf + 3500, suffix) == 0);
+    }
+}
+
+/* Test with long strings and wide string result.  */
+static void
+test_wide_long (const char *mbs, const wchar_t *wide, const size_t *length)
+{
+  wchar_t buf[2000];
+  _Static_assert (sizeof (buf) > sizeof (wchar_t) * WIDE_STRING_LENGTH,
+                  "buffer size consistent with string length");
+  const wchar_t *suffix = L"||TERM";
+  TEST_VERIFY_EXIT (sizeof (buf)
+                    > length[WIDE_STRING_LENGTH] + wcslen (suffix));
+
+  /* Test formatting of the entire string.  */
+  {
+    int ret = swprintf (buf, sizeof (buf), L"%s%ls", mbs, suffix);
+    TEST_VERIFY (ret == WIDE_STRING_LENGTH + wcslen (suffix));
+    TEST_VERIFY (wmemcmp (buf, wide, WIDE_STRING_LENGTH) == 0);
+    TEST_VERIFY (wcscmp (buf + WIDE_STRING_LENGTH, suffix) == 0);
+
+    /* Left-justified string, printed in full.  */
+    ret = swprintf (buf, sizeof (buf), L"%-1500s%ls", mbs, suffix);
+    TEST_VERIFY (ret == 1500 + wcslen (suffix));
+    TEST_VERIFY (wmemcmp (buf, wide, WIDE_STRING_LENGTH) == 0);
+    for (size_t i = WIDE_STRING_LENGTH; i < 1500; ++i)
+      TEST_VERIFY (buf[i] == L' ');
+    TEST_VERIFY (wcscmp (buf + 1500, suffix) == 0);
+
+    /* Right-justified string, printed in full.   */
+    ret = swprintf (buf, sizeof (buf), L"%1500s%ls", mbs, suffix);
+    TEST_VERIFY (ret == 1500 + wcslen (suffix));
+    size_t padding = 1500 - WIDE_STRING_LENGTH;
+    for (size_t i = 0; i < padding; ++i)
+      TEST_VERIFY (buf[i] == ' ');
+    TEST_VERIFY (wmemcmp (buf + padding, wide, WIDE_STRING_LENGTH) == 0);
+    TEST_VERIFY (wcscmp (buf + 1500, suffix) == 0);
+  }
+
+  for (int wide_len = 0; wide_len <= WIDE_STRING_LENGTH + 1; ++wide_len)
+    {
+      size_t actual_wide_len;
+      if (wide_len < WIDE_STRING_LENGTH)
+        actual_wide_len = wide_len;
+      else
+        actual_wide_len = WIDE_STRING_LENGTH;
+      if (test_verbose > 0)
+        printf ("info: %s: wide_len=%d actual_wide_len=%zu\n",
+                __func__, wide_len, actual_wide_len);
+
+      int ret = swprintf (buf, sizeof (buf), L"%.*s%ls",
+                          wide_len, mbs, suffix);
+      TEST_VERIFY (ret == actual_wide_len + wcslen (suffix));
+      TEST_VERIFY (wmemcmp (buf, wide, actual_wide_len) == 0);
+      TEST_VERIFY (wcscmp (buf + actual_wide_len, suffix) == 0);
+
+      /* Left-justified string, printed in full.  */
+      ret = swprintf (buf, sizeof (buf), L"%-1500.*s%ls",
+                      wide_len, mbs, suffix);
+      TEST_VERIFY (ret == 1500 + wcslen (suffix));
+      TEST_VERIFY (wmemcmp (buf, wide, actual_wide_len) == 0);
+      for (size_t i = actual_wide_len; i < 1500; ++i)
+        TEST_VERIFY (buf[i] == L' ');
+      TEST_VERIFY (wcscmp (buf + 1500, suffix) == 0);
+
+      /* Right-justified string, printed in full.   */
+      ret = swprintf (buf, sizeof (buf), L"%1500.*s%ls",
+                      wide_len, mbs, suffix);
+      TEST_VERIFY (ret == 1500 + wcslen (suffix));
+      size_t padding = 1500 - actual_wide_len;
+      for (size_t i = 0; i < padding; ++i)
+        TEST_VERIFY (buf[i] == L' ');
+      TEST_VERIFY (wmemcmp (buf + padding, wide, actual_wide_len) == 0);
+      TEST_VERIFY (wcscmp (buf + 1500, suffix) == 0);
+    }
+}
+
+static int
+do_test (void)
+{
+  /* This test only covers UTF-8 as a multi-byte character set.  A
+     locale with a multi-byte character set with shift state would be
+     a relevant test target as well, but glibc currently does not ship
+     such a locale.  */
+  TEST_VERIFY (setlocale (LC_CTYPE, "de_DE.UTF-8") != NULL);
+
+  test_mbs_result ();
+  test_wide_result ();
+
+  char *mbs;
+  wchar_t *wide;
+  size_t *length;
+  make_random_string (&mbs, &wide, &length);
+  TEST_VERIFY (strlen (mbs) == length[WIDE_STRING_LENGTH]);
+  if (test_verbose > 0)
+    printf ("info: long multi-byte string contains %zu characters\n",
+            length[WIDE_STRING_LENGTH]);
+  test_mbs_long (mbs, wide, length);
+  test_wide_long (mbs, wide, length);
+  free (mbs);
+  free (wide);
+  free (length);
+
+  return 0;
+}
+
+#include <support/test-driver.c>
