diff --git a/ChangeLog b/ChangeLog
index f2bf802688..1eaddc5728 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun May 15 23:53:31 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
+
+	* include/ruby/intern.h: resurrect old rb_fd_copy().
+	* thread.c (rb_fd_copy): ditto.
+
 Sun May 15 23:45:11 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
 	* include/ruby/intern.h: remove rb_fd_copy() to rb_fd_dup() and
diff --git a/include/ruby/intern.h b/include/ruby/intern.h
index ca8f7b984a..71fc3fcb2c 100644
--- a/include/ruby/intern.h
+++ b/include/ruby/intern.h
@@ -250,6 +250,7 @@ void rb_fd_zero(rb_fdset_t *);
 void rb_fd_set(int, rb_fdset_t *);
 void rb_fd_clr(int, rb_fdset_t *);
 int rb_fd_isset(int, const rb_fdset_t *);
+void rb_fd_copy(rb_fdset_t *, const fd_set *, int);
 void rb_fd_dup(rb_fdset_t *dst, const rb_fdset_t *src);
 int rb_fd_select(int, rb_fdset_t *, rb_fdset_t *, rb_fdset_t *, struct timeval *);
 
@@ -284,6 +285,7 @@ typedef fd_set rb_fdset_t;
 #define rb_fd_set(n, f)	FD_SET((n), (f))
 #define rb_fd_clr(n, f)	FD_CLR((n), (f))
 #define rb_fd_isset(n, f) FD_ISSET((n), (f))
+#define rb_fd_copy(d, s, n) (*(d) = *(s))
 #define rb_fd_dup(d, s) (*(d) = *(s))
 #define rb_fd_resize(n, f)	((void)(f))
 #define rb_fd_ptr(f)	(f)
diff --git a/thread.c b/thread.c
index 88c396e185..6f7118de47 100644
--- a/thread.c
+++ b/thread.c
@@ -2391,6 +2391,17 @@ rb_fd_isset(int n, const rb_fdset_t *fds)
     return FD_ISSET(n, fds->fdset) != 0; /* "!= 0" avoids FreeBSD PR 91421 */
 }
 
+void
+rb_fd_copy(rb_fdset_t *dst, const fd_set *src, int max)
+{
+    size_t size = howmany(max, NFDBITS) * sizeof(fd_mask);
+
+    if (size < sizeof(fd_set)) size = sizeof(fd_set);
+    dst->maxfd = max;
+    dst->fdset = xrealloc(dst->fdset, size);
+    memcpy(dst->fdset, src, size);
+}
+
 void
 rb_fd_dup(rb_fdset_t *dst, const rb_fdset_t *src)
 {