diff --git a/ChangeLog b/ChangeLog
index 016c974645..36c62566bf 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sat Jan 18 22:35:15 2014  Tanaka Akira  <akr@fsij.org>
+
+	* io.c (rb_update_max_fd): Return immediately if the given fd is small
+	  enough.
+
 Sat Jan 18 22:25:53 2014  Tanaka Akira  <akr@fsij.org>
 
 	* io.c: Test O_CLOEXEC only once.
diff --git a/io.c b/io.c
index 5d66bdf4b0..6bab4f9378 100644
--- a/io.c
+++ b/io.c
@@ -189,6 +189,9 @@ rb_update_max_fd(int fd)
     struct stat buf;
     rb_atomic_t afd = (rb_atomic_t)fd;
 
+    if (afd <= max_file_descriptor)
+        return;
+
     if (fstat(fd, &buf) != 0 && errno == EBADF) {
         rb_bug("rb_update_max_fd: invalid fd (%d) given.", fd);
     }