diff --git a/ChangeLog b/ChangeLog
index a67a52ec0f..e36c9314e7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Thu Oct 15 09:25:07 2009  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* ext/socket/init.c (rsock_init_sock): mswin doesn't have S_IFSOCK
+	  flag in st_mode of struct stat. so, use rb_w32_issocket() function
+	  instead of S_ISSOCK macro.
+
 Thu Oct 15 00:47:42 2009  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* tool/enc-unicode.rb,
diff --git a/ext/socket/init.c b/ext/socket/init.c
index 85cc3de4f9..b143dccd5f 100644
--- a/ext/socket/init.c
+++ b/ext/socket/init.c
@@ -45,10 +45,15 @@ rsock_init_sock(VALUE sock, int fd)
     rb_io_t *fp;
     struct stat sbuf;
 
+#ifndef _WIN32
     if (fstat(fd, &sbuf) < 0)
         rb_sys_fail(0);
     if (!S_ISSOCK(sbuf.st_mode))
         rb_raise(rb_eArgError, "not a socket file descriptor");
+#else
+    if (!rb_w32_is_socket(fd))
+        rb_raise(rb_eArgError, "not a socket file descriptor");
+#endif
 
     MakeOpenFile(sock, fp);
     fp->fd = fd;