diff --git a/ChangeLog b/ChangeLog
index 3b264b63e2..27aa83aba1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Jun 16 16:35:35 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* class.c (Init_class_hierarchy): prevent rb_cObject which is the
+	  class tree root, from GC.  [ruby-dev:49666] [Bug #12492]
+
 Thu Jun 16 12:17:52 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* string.c (tr_trans): adjust buffer size by processed and rest
diff --git a/class.c b/class.c
index 1215b6d93d..6b818a326f 100644
--- a/class.c
+++ b/class.c
@@ -547,6 +547,7 @@ Init_class_hierarchy(void)
 {
     rb_cBasicObject = boot_defclass("BasicObject", 0);
     rb_cObject = boot_defclass("Object", rb_cBasicObject);
+    rb_gc_register_mark_object(rb_cObject);
 
     /* resolve class name ASAP for order-independence */
     rb_class_name(rb_cObject);