diff --git a/ChangeLog b/ChangeLog
index 5d19e8a3e4..4d52135bff 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+Wed Feb 11 18:09:41 2009  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* gc.c (define_final, undefine_final): shouldn't add/remove finalizer
+	  of forzen objects.
+
+	* gc.c (undefine_final): should remove FL_FINALIZE flag.
+	  [ruby-dev:37964] (also see [ruby-dev:37959])
+
 Wed Feb 11 17:37:41 2009  Tanaka Akira  <akr@fsij.org>
 
 	* ext/socket/lib/socket.rb (Socket.udp_server_sockets): call the block
diff --git a/gc.c b/gc.c
index 784949cf9e..998772d150 100644
--- a/gc.c
+++ b/gc.c
@@ -2261,9 +2261,11 @@ static VALUE
 undefine_final(VALUE os, VALUE obj)
 {
     rb_objspace_t *objspace = &rb_objspace;
+    if (OBJ_FROZEN(obj)) rb_error_frozen("object");
     if (finalizer_table) {
 	st_delete(finalizer_table, (st_data_t*)&obj, 0);
     }
+    FL_UNSET(obj, FL_FINALIZE);
     return obj;
 }
 
@@ -2283,6 +2285,7 @@ define_final(int argc, VALUE *argv, VALUE os)
     VALUE obj, block, table;
 
     rb_scan_args(argc, argv, "11", &obj, &block);
+    if (OBJ_FROZEN(obj)) rb_error_frozen("object");
     if (argc == 1) {
 	block = rb_block_proc();
     }