diff --git a/ChangeLog b/ChangeLog
index 968e24e961..274e245ebb 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+Thu Dec 10 09:20:58 2009  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* encoding.c (Init_Encoding): undef Encoding.new because
+	  a class which is rb_undef_alloc-func-ed can't call new method.
+	  [ruby-dev:39862]
+
+	* vm.c (Init_VM): undef RubyVM.new and RubyVM::Env.new.
+
 Mon Dec 21 17:51:44 2009  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* regcomp.c (optimize_node_left): include equal on the condition of for-loop.
diff --git a/encoding.c b/encoding.c
index 22a03d0ae4..6b7c5a5c20 100644
--- a/encoding.c
+++ b/encoding.c
@@ -1505,6 +1505,7 @@ Init_Encoding(void)
 
     rb_cEncoding = rb_define_class("Encoding", rb_cObject);
     rb_undef_alloc_func(rb_cEncoding);
+    rb_undef_method(CLASS_OF(rb_cEncoding), "new");
     rb_define_method(rb_cEncoding, "to_s", enc_name, 0);
     rb_define_method(rb_cEncoding, "inspect", enc_inspect, 0);
     rb_define_method(rb_cEncoding, "name", enc_name, 0);
diff --git a/vm.c b/vm.c
index fa028fd187..e522c9f300 100644
--- a/vm.c
+++ b/vm.c
@@ -1944,6 +1944,7 @@ Init_VM(void)
     /* ::VM */
     rb_cRubyVM = rb_define_class("RubyVM", rb_cObject);
     rb_undef_alloc_func(rb_cRubyVM);
+    rb_undef_method(CLASS_OF(rb_cRubyVM), "new");
 
     /* ::VM::FrozenCore */
     fcore = rb_class_new(rb_cBasicObject);
@@ -1962,6 +1963,7 @@ Init_VM(void)
     /* ::VM::Env */
     rb_cEnv = rb_define_class_under(rb_cRubyVM, "Env", rb_cObject);
     rb_undef_alloc_func(rb_cEnv);
+    rb_undef_method(CLASS_OF(rb_cEnv), "new");
 
     /* ::Thread */
     rb_cThread = rb_define_class("Thread", rb_cObject);