diff --git a/ChangeLog b/ChangeLog
index 1f55a98a9d..07428626b3 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sat Mar 31 21:39:45 2012  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* lib/webrick/utils.rb (WEBrick::Utils::TimeoutHandler): dup to prevent
+	  @timeout_info's "can't add a new key into hash during iteration".
+
 Sat Mar 31 14:22:59 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* hash.c (hash_default_value): extract from rb_hash_aref(), to be
diff --git a/lib/webrick/utils.rb b/lib/webrick/utils.rb
index 157c530cc9..d9c39360ee 100644
--- a/lib/webrick/utils.rb
+++ b/lib/webrick/utils.rb
@@ -175,7 +175,7 @@ module WEBrick
         Thread.start{
           while true
             now = Time.now
-            @timeout_info.each{|thread, ary|
+            @timeout_info.dup.each{|thread, ary|
               ary.dup.each{|info|
                 time, exception = *info
                 interrupt(thread, info.object_id, exception) if time < now