diff --git a/libio/Makefile b/libio/Makefile
index cd5a3afeeb..4370152964 100644
--- a/libio/Makefile
+++ b/libio/Makefile
@@ -86,6 +86,8 @@ tests = \
   bug-wmemstream1 \
   bug-wsetpos \
   test-fmemopen \
+  test-fputs-unbuffered-full \
+  test-fputws-unbuffered-full \
   tst-atime \
   tst-bz22415 \
   tst-bz24051 \
diff --git a/libio/test-fputs-unbuffered-full.c b/libio/test-fputs-unbuffered-full.c
new file mode 100644
index 0000000000..145b4b6a57
--- /dev/null
+++ b/libio/test-fputs-unbuffered-full.c
@@ -0,0 +1,78 @@
+/* Regression test for 20632.
+   Copyright (C) 2024 Free Software Foundation, Inc.
+   Copyright The GNU Toolchain Authors.
+   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
+   <https://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <support/check.h>
+#include <support/xunistd.h>
+#include <unistd.h>
+
+#ifndef WIDE
+# define TEST_NAME "fputs-unbuffered-full"
+# define CHAR char
+# define FPUTS fputs
+# define TEXT "0123456789ABCDEF"
+#else
+# include <wchar.h>
+# define TEST_NAME "fputws-unbuffered-full"
+# define CHAR wchar_t
+# define FPUTS fputws
+# define TEXT L"0123456789ABCDEF"
+#endif /* WIDE */
+
+
+static int
+do_test (void)
+{
+  /* Open an unbuffered stream to /dev/full.  */
+  FILE *fp = fopen ("/dev/full", "w");
+  TEST_VERIFY_EXIT (fp != NULL);
+  int ret = setvbuf (fp, NULL, _IONBF, 0);
+  TEST_VERIFY_EXIT (ret == 0);
+
+  /* Output a long string. */
+  const int sz = 4096;
+  CHAR *buff = calloc (sz+1, sizeof *buff);
+  for (int i=0; i < sz; i++)
+    buff[i] = (CHAR) 'x';
+  buff[sz] = (CHAR) '\0';
+  errno = 0;
+  ret = FPUTS (buff, fp);
+  TEST_VERIFY (ret == EOF);
+  TEST_VERIFY (errno == ENOSPC);
+  free (buff);
+
+  /* Output shorter strings.   */
+  for (int i=0; i < 1024; i++)
+    {
+      errno = 0;
+      ret = FPUTS (TEXT, fp);
+      TEST_VERIFY (ret == EOF);
+      TEST_VERIFY (errno == ENOSPC);
+
+      /* Call malloc, triggering a crash if its
+         function pointers have been overwritten.  */
+      void *volatile ptr = malloc (1);
+      free (ptr);
+    }
+  return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/libio/test-fputws-unbuffered-full.c b/libio/test-fputws-unbuffered-full.c
new file mode 100644
index 0000000000..f3d79326e4
--- /dev/null
+++ b/libio/test-fputws-unbuffered-full.c
@@ -0,0 +1,21 @@
+/* Regression test for 20632.
+   Copyright (C) 2024 Free Software Foundation, Inc.
+   Copyright The GNU Toolchain Authors.
+   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
+   <https://www.gnu.org/licenses/>.  */
+
+#define WIDE 1
+#include "./test-fputs-unbuffered-full.c"
diff --git a/libio/wfileops.c b/libio/wfileops.c
index 6de5968358..fdbe8692e8 100644
--- a/libio/wfileops.c
+++ b/libio/wfileops.c
@@ -420,14 +420,14 @@ _IO_wfile_overflow (FILE *f, wint_t wch)
 	{
 	  _IO_wdoallocbuf (f);
 	  _IO_free_wbackup_area (f);
-	  _IO_wsetg (f, f->_wide_data->_IO_buf_base,
-		     f->_wide_data->_IO_buf_base, f->_wide_data->_IO_buf_base);
 
 	  if (f->_IO_write_base == NULL)
 	    {
 	      _IO_doallocbuf (f);
 	      _IO_setg (f, f->_IO_buf_base, f->_IO_buf_base, f->_IO_buf_base);
 	    }
+	  _IO_wsetg (f, f->_wide_data->_IO_buf_base,
+		     f->_wide_data->_IO_buf_base, f->_wide_data->_IO_buf_base);
 	}
       else
 	{
@@ -958,7 +958,7 @@ _IO_wfile_xsputn (FILE *f, const void *data, size_t n)
   const wchar_t *s = (const wchar_t *) data;
   size_t to_do = n;
   int must_flush = 0;
-  size_t count;
+  size_t count = 0;
 
   if (n <= 0)
     return 0;
@@ -967,7 +967,6 @@ _IO_wfile_xsputn (FILE *f, const void *data, size_t n)
      (or the filebuf is unbuffered), use sys_write directly. */
 
   /* First figure out how much space is available in the buffer. */
-  count = f->_wide_data->_IO_write_end - f->_wide_data->_IO_write_ptr;
   if ((f->_flags & _IO_LINE_BUF) && (f->_flags & _IO_CURRENTLY_PUTTING))
     {
       count = f->_wide_data->_IO_buf_end - f->_wide_data->_IO_write_ptr;
@@ -985,6 +984,10 @@ _IO_wfile_xsputn (FILE *f, const void *data, size_t n)
 	    }
 	}
     }
+  else if (f->_wide_data->_IO_write_end > f->_wide_data->_IO_write_ptr)
+    count = f->_wide_data->_IO_write_end
+      - f->_wide_data->_IO_write_ptr; /* Space available.  */
+
   /* Then fill the buffer. */
   if (count > 0)
     {