diff --git a/ChangeLog b/ChangeLog
index ce7364f215..1c390e2742 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue May  6 00:29:21 2008  Yukihiro Matsumoto  <matz@ruby-lang.org>
+
+	* iseq.c (insn_operand_intern): should handle Qundef embedded in
+	  operand.  [ruby-core:16656]
+
 Tue May  6 00:00:02 2008  Yukihiro Matsumoto  <matz@ruby-lang.org>
 
 	* compile.c (iseq_compile_each): should call compile_cpath() for
diff --git a/iseq.c b/iseq.c
index f475ca7a37..98eaa03c3a 100644
--- a/iseq.c
+++ b/iseq.c
@@ -660,9 +660,14 @@ insn_operand_intern(rb_iseq_t *iseq,
       case TS_ID:		/* ID (symbol) */
 	op = ID2SYM(op);
       case TS_VALUE:		/* VALUE */
-	ret = rb_inspect(op);
-	if (CLASS_OF(op) == rb_cISeq) {
-	    rb_ary_push(child, op);
+	if (op == Qundef) {
+	    ret = rb_str_new2("undef");
+	}
+	else {
+	    ret = rb_inspect(op);
+	    if (CLASS_OF(op) == rb_cISeq) {
+		rb_ary_push(child, op);
+	    }
 	}
 	break;