diff --git a/ChangeLog b/ChangeLog
index 58f90576fe..1c166c1106 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri Jun  3 19:58:14 2011  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* io.c (io_fflush): windows -- call fsync() only when the FD is tied to
+	  file, because if the FD is pipe, it blocks.
+
 Fri Jun  3 09:27:31 2011  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* lib/net/http.rb (URI::HTTP#request_uri): return nil when the uri
diff --git a/io.c b/io.c
index f9fc3724f3..12002be927 100644
--- a/io.c
+++ b/io.c
@@ -683,7 +683,9 @@ io_fflush(rb_io_t *fptr)
         rb_io_check_closed(fptr);
     }
 #ifdef _WIN32
-    fsync(fptr->fd);
+    if (GetFileType((HANDLE)rb_w32_get_osfhandle(fptr->fd)) == FILE_TYPE_DISK) {
+	fsync(fptr->fd);
+    }
 #endif
     return 0;
 }
@@ -1368,8 +1370,10 @@ rb_io_fsync(VALUE io)
 
     if (io_fflush(fptr) < 0)
         rb_sys_fail(0);
+#ifndef _WIN32	/* already called in io_fflush() */
     if (fsync(fptr->fd) < 0)
 	rb_sys_fail_path(fptr->pathv);
+#endif
     return INT2FIX(0);
 }
 #else