diff --git a/ChangeLog b/ChangeLog
index 3c713064e1..849a6f5d1f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,8 +1,12 @@
+Mon Jun 13 12:23:39 2011  NARUSE, Yui  <naruse@ruby-lang.org>
+
 Mon Jun 13 12:23:39 2011  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* ext/psych/lib/psych/deprecated.rb (Object#to_yaml_properties):
 	  undef to_yaml_properties before redefine it.
 
+	* ext/syck/lib/syck/rubytypes.rb: ditto.
+
 Mon Jun 13 11:30:10 2011  Martin Bosslet  <Martin.Bosslet@googlemail.com>
 
 	* ext/openssl/ossl_digest.c: allow Digests to be created by sn, ln or
diff --git a/ext/syck/lib/syck/rubytypes.rb b/ext/syck/lib/syck/rubytypes.rb
index 31b1e2b804..90f1cbfacf 100644
--- a/ext/syck/lib/syck/rubytypes.rb
+++ b/ext/syck/lib/syck/rubytypes.rb
@@ -10,6 +10,7 @@ end
 class Object
     yaml_as "tag:ruby.yaml.org,2002:object"
     def to_yaml_style; end
+    undef to_yaml_properties
     def to_yaml_properties; instance_variables.sort; end
 	def to_yaml( opts = {} )
 		YAML::quick_emit( self, opts ) do |out|