diff --git a/ChangeLog b/ChangeLog
index e2b28502d8..a4bd327c35 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sat Dec 25 20:01:40 2010  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
+
+	* io.c (pipe_open): Added rb_thread_atfork(). We must reinitialize
+	  GVL at new process creation.
+
 Sat Dec 25 18:26:55 2010  Tanaka Akira  <akr@fsij.org>
 
 	* ext/socket/option.c (inspect_ipv6_mreq): new function to inspect
diff --git a/io.c b/io.c
index 5e38ce7db2..943d124988 100644
--- a/io.c
+++ b/io.c
@@ -5072,6 +5072,7 @@ pipe_open(struct rb_exec_arg *eargp, VALUE prog, const char *modestr, int fmode,
 	fflush(stdin);		/* is it really needed? */
 	pid = rb_fork(&status, 0, 0, Qnil);
 	if (pid == 0) {		/* child */
+	    rb_thread_atfork();
 	    popen_redirect(&arg);
 	    rb_io_synchronized(RFILE(orig_stdout)->fptr);
 	    rb_io_synchronized(RFILE(orig_stderr)->fptr);