diff --git a/ChangeLog b/ChangeLog
index 7a08141caf..32dad4c028 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon Jul 26 13:01:25 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* vm.c (rb_thread_mark): should mark iseq itself other than normal
+	  iseq.  [ruby-dev:41880]
+
 Mon Jul 26 11:51:01 2010  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* configure.in: define BROKEN_CLOSE on FreeBSD.
diff --git a/vm.c b/vm.c
index 3010fe8ef3..e62c9a4b7b 100644
--- a/vm.c
+++ b/vm.c
@@ -1646,8 +1646,11 @@ rb_thread_mark(void *ptr)
 	    rb_gc_mark_locations(p, p + th->mark_stack_len);
 
 	    while (cfp != limit_cfp) {
+		rb_iseq_t *iseq = cfp->iseq;
 		rb_gc_mark(cfp->proc);
-		if (RUBY_VM_NORMAL_ISEQ_P(cfp->iseq)) rb_gc_mark(cfp->iseq->self);
+		if (iseq) {
+		    rb_gc_mark(RUBY_VM_NORMAL_ISEQ_P(iseq) ? iseq->self : (VALUE)iseq);
+		}
 		if (cfp->me) ((rb_method_entry_t *)cfp->me)->mark = 1;
 		cfp = RUBY_VM_PREVIOUS_CONTROL_FRAME(cfp);
 	    }