diff --git a/nt/ChangeLog b/nt/ChangeLog
index c0598dd5630..23c0c74b6f1 100644
--- a/nt/ChangeLog
+++ b/nt/ChangeLog
@@ -1,3 +1,12 @@
+2013-08-04  Eli Zaretskii  <eliz@gnu.org>
+
+	* mingw-cfg.site (ac_cv_func_mkostemp): New var with value of
+	"yes".
+
+	* inc/ms-w32.h (mkostemp): Declare prototype.
+
+	* config.nt (HAVE_MKOSTEMP): Define to 1.  (Bug#15015)
+
 2013-07-07  Eli Zaretskii  <eliz@gnu.org>
 
 	* inc/sys/socket.h (F_SETFD, O_CLOEXEC, F_DUPFD_CLOEXEC)
diff --git a/nt/config.nt b/nt/config.nt
index 95b56f2dc64..3ba60a85752 100644
--- a/nt/config.nt
+++ b/nt/config.nt
@@ -796,6 +796,9 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
    systems that support xmenu.c. */
 #undef HAVE_MENUS
 
+/* Define to 1 if you have the `mkostemp' function. */
+#define HAVE_MKOSTEMP 1
+
 /* Define to 1 if you have the `mkstemp' function. */
 #undef HAVE_MKSTEMP
 
diff --git a/nt/inc/ms-w32.h b/nt/inc/ms-w32.h
index 3e50c78f145..f01f254d81c 100644
--- a/nt/inc/ms-w32.h
+++ b/nt/inc/ms-w32.h
@@ -450,6 +450,8 @@ extern int getpagesize (void);
 
 extern void * memrchr (void const *, int, size_t);
 
+extern int mkostemp (char *, int);
+
 
 #if defined (__MINGW32__)
 
diff --git a/nt/mingw-cfg.site b/nt/mingw-cfg.site
index cf55fe04ed8..325bba29ae5 100644
--- a/nt/mingw-cfg.site
+++ b/nt/mingw-cfg.site
@@ -60,6 +60,7 @@ ac_cv_func_getpeername=yes
 # Implemented as sys_socket in w32.c
 ac_cv_func_socket=yes
 # Implemented in w32.c
+ac_cv_func_mkostemp=yes
 ac_cv_func_readlink=yes
 ac_cv_func_symlink=yes
 # Avoid run-time tests of readlink and symlink, which will fail
diff --git a/src/ChangeLog b/src/ChangeLog
index 8a9de96358d..0fe6b4e6ce3 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,9 @@
+2013-08-04  Eli Zaretskii  <eliz@gnu.org>
+
+	* w32.c (mkostemp): New function.
+	(mktemp): Remove, no longer used.  Most of the code reused in
+	mkostemp.  (Bug#15015)
+
 2013-08-04  Dmitry Antipov  <dmantipov@yandex.ru>
 
 	* dispnew.c (glyph_matrix_count, glyph_pool_count):
diff --git a/src/w32.c b/src/w32.c
index fb2d7c75972..af42c6f39c2 100644
--- a/src/w32.c
+++ b/src/w32.c
@@ -3414,56 +3414,6 @@ sys_mkdir (const char * path)
   return _mkdir (map_w32_filename (path, NULL));
 }
 
-/* Because of long name mapping issues, we need to implement this
-   ourselves.  Also, MSVC's _mktemp returns NULL when it can't generate
-   a unique name, instead of setting the input template to an empty
-   string.
-
-   Standard algorithm seems to be use pid or tid with a letter on the
-   front (in place of the 6 X's) and cycle through the letters to find a
-   unique name.  We extend that to allow any reasonable character as the
-   first of the 6 X's.  */
-char *
-sys_mktemp (char * template)
-{
-  char * p;
-  int i;
-  unsigned uid = GetCurrentThreadId ();
-  static char first_char[] = "abcdefghijklmnopqrstuvwyz0123456789!%-_@#";
-
-  if (template == NULL)
-    return NULL;
-  p = template + strlen (template);
-  i = 5;
-  /* replace up to the last 5 X's with uid in decimal */
-  while (--p >= template && p[0] == 'X' && --i >= 0)
-    {
-      p[0] = '0' + uid % 10;
-      uid /= 10;
-    }
-
-  if (i < 0 && p[0] == 'X')
-    {
-      i = 0;
-      do
-	{
-	  int save_errno = errno;
-	  p[0] = first_char[i];
-	  if (faccessat (AT_FDCWD, template, F_OK, AT_EACCESS) < 0)
-	    {
-	      errno = save_errno;
-	      return template;
-	    }
-	}
-      while (++i < sizeof (first_char));
-    }
-
-  /* Template is badly formed or else we can't generate a unique name,
-     so return empty string */
-  template[0] = 0;
-  return template;
-}
-
 int
 sys_open (const char * path, int oflag, int mode)
 {
@@ -3481,6 +3431,61 @@ sys_open (const char * path, int oflag, int mode)
   return res;
 }
 
+/* Implementation of mkostemp for MS-Windows, to avoid race conditions
+   when using mktemp.
+
+   Standard algorithm for generating a temporary file name seems to be
+   use pid or tid with a letter on the front (in place of the 6 X's)
+   and cycle through the letters to find a unique name.  We extend
+   that to allow any reasonable character as the first of the 6 X's,
+   so that the number of simultaneously used temporary files will be
+   greater.  */
+
+int
+mkostemp (char * template, int flags)
+{
+  char * p;
+  int i, fd = -1;
+  unsigned uid = GetCurrentThreadId ();
+  int save_errno = errno;
+  static char first_char[] = "abcdefghijklmnopqrstuvwyz0123456789!%-_@#";
+
+  errno = EINVAL;
+  if (template == NULL)
+    return -1;
+
+  p = template + strlen (template);
+  i = 5;
+  /* replace up to the last 5 X's with uid in decimal */
+  while (--p >= template && p[0] == 'X' && --i >= 0)
+    {
+      p[0] = '0' + uid % 10;
+      uid /= 10;
+    }
+
+  if (i < 0 && p[0] == 'X')
+    {
+      i = 0;
+      do
+	{
+	  p[0] = first_char[i];
+	  if ((fd = sys_open (template,
+			      flags | _O_CREAT | _O_EXCL | _O_RDWR,
+			      S_IRUSR | S_IWUSR)) >= 0
+	      || errno != EEXIST)
+	    {
+	      if (fd >= 0)
+		errno = save_errno;
+	      return fd;
+	    }
+	}
+      while (++i < sizeof (first_char));
+    }
+
+  /* Template is badly formed or else we can't generate a unique name.  */
+  return -1;
+}
+
 int
 fchmod (int fd, mode_t mode)
 {