diff --git a/ChangeLog b/ChangeLog
index 6f70211c2b..044dcaae9d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon Mar 18 01:14:56 2013  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* io.c (io_fillbuf): show fd number on failure to debug.
+	  http://c5632.rubyci.org/~chkbuild/ruby-trunk/log/20130316T050302Z.diff.html.gz
+
 Sun Mar 17 02:38:21 2013  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
 	* ext/date/date_core.c: include sys/time.h for avoiding implicit
diff --git a/io.c b/io.c
index 8d70ed41c6..eb8b80c63b 100644
--- a/io.c
+++ b/io.c
@@ -1657,7 +1657,13 @@ io_fillbuf(rb_io_t *fptr)
         if (r < 0) {
             if (rb_io_wait_readable(fptr->fd))
                 goto retry;
-            rb_sys_fail_path(fptr->pathv);
+	    {
+		VALUE path = rb_sprintf("fd:%d ", fptr->fd);
+		if (!NIL_P(fptr->pathv)) {
+		    rb_str_append(path, fptr->pathv);
+		}
+		rb_sys_fail_path(path);
+	    }
         }
         fptr->rbuf.off = 0;
         fptr->rbuf.len = (int)r; /* r should be <= rbuf_capa */