diff --git a/ChangeLog b/ChangeLog
index 26c51687e6..f5b71a2760 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Jun 18 23:38:07 2015  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* thread.c (rb_thread_safe_level): fix document.  $SAFE=3 is obsolete.
+	  [ci skip]
+
 Thu Jun 18 23:25:51 2015  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* ext/extmk.rb: configure intersection of with-ext and not
diff --git a/thread.c b/thread.c
index 8e8d8fbdfe..f80fcf6bf4 100644
--- a/thread.c
+++ b/thread.c
@@ -2701,9 +2701,9 @@ rb_thread_stop_p(VALUE thread)
  *  Returns the safe level in effect for <i>thr</i>. Setting thread-local safe
  *  levels can help when implementing sandboxes which run insecure code.
  *
- *     thr = Thread.new { $SAFE = 3; sleep }
+ *     thr = Thread.new { $SAFE = 1; sleep }
  *     Thread.current.safe_level   #=> 0
- *     thr.safe_level              #=> 3
+ *     thr.safe_level              #=> 1
  */
 
 static VALUE