diff --git a/ChangeLog b/ChangeLog
index 610fa80353..0f0d30a245 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Wed Jun 24 16:54:11 2015  Koichi Sasada  <ko1@atdot.net>
+
+	* gc.c (gc_mark_children): add additional debug code for #11244.
+
 Wed Jun 24 16:05:42 2015  Eric Wong  <e@80x24.org>
 
 	* string.c (rb_str_justify): use RB_GC_GUARD
diff --git a/gc.c b/gc.c
index 9b1870276c..d5719fe7b1 100644
--- a/gc.c
+++ b/gc.c
@@ -4304,6 +4304,10 @@ gc_mark_children(rb_objspace_t *objspace, VALUE obj)
 	if (!RCLASS_EXT(obj)) break;
 	mark_tbl(objspace, RCLASS_IV_TBL(obj));
 	mark_const_tbl(objspace, RCLASS_CONST_TBL(obj));
+
+	/* TODO: remove it. check code for Bug #11244 */
+	if (RB_TYPE_P(RCLASS_SUPER(obj), T_NONE)) rb_bug("gc_mark_children: super is T_NONE (%s)", obj_info(obj));
+
 	gc_mark(objspace, RCLASS_SUPER((VALUE)obj));
 	break;