diff --git a/ChangeLog b/ChangeLog
index 0a25a307e5..bda2481738 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+Tue Jul 21 19:43:20 2015  Koichi Sasada  <ko1@atdot.net>
+
+	* compile.c: constify the first parameter (iseq).
+	  * iseq_add_mark_object()
+	  * iseq_add_mark_object_compile_time()
+
+	* iseq.c, iseq.h (rb_iseq_add_mark_object): ditto.
+
 Tue Jul 21 16:18:48 2015  Eric Wong  <e@80x24.org>
 
 	* test/socket/test_nonblock.rb: increase buffer sizes
diff --git a/compile.c b/compile.c
index a61c5866af..e6b00e55bb 100644
--- a/compile.c
+++ b/compile.c
@@ -422,7 +422,7 @@ APPEND_ELEM(ISEQ_ARG_DECLARE LINK_ANCHOR *anchor, LINK_ELEMENT *before, LINK_ELE
 #endif
 
 static int
-iseq_add_mark_object(rb_iseq_t *iseq, VALUE v)
+iseq_add_mark_object(const rb_iseq_t *iseq, VALUE v)
 {
     if (!SPECIAL_CONST_P(v)) {
 	rb_iseq_add_mark_object(iseq, v);
@@ -433,7 +433,7 @@ iseq_add_mark_object(rb_iseq_t *iseq, VALUE v)
 #define ruby_sourcefile		RSTRING_PTR(iseq->location.path)
 
 static int
-iseq_add_mark_object_compile_time(rb_iseq_t *iseq, VALUE v)
+iseq_add_mark_object_compile_time(const rb_iseq_t *iseq, VALUE v)
 {
     if (!SPECIAL_CONST_P(v)) {
 	rb_ary_push(iseq->compile_data->mark_ary, v);
diff --git a/iseq.c b/iseq.c
index 774aafadda..1af491e997 100644
--- a/iseq.c
+++ b/iseq.c
@@ -229,7 +229,7 @@ set_relation(rb_iseq_t *iseq, const VALUE parent)
 }
 
 void
-rb_iseq_add_mark_object(rb_iseq_t *iseq, VALUE obj)
+rb_iseq_add_mark_object(const rb_iseq_t *iseq, VALUE obj)
 {
     if (!RTEST(iseq->mark_ary)) {
 	RB_OBJ_WRITE(iseq->self, &iseq->mark_ary, rb_ary_tmp_new(3));
diff --git a/iseq.h b/iseq.h
index b4008c384b..487b703c80 100644
--- a/iseq.h
+++ b/iseq.h
@@ -23,7 +23,7 @@ VALUE rb_iseq_build_from_ary(rb_iseq_t *iseq, VALUE misc,
 			     VALUE exception, VALUE body);
 
 /* iseq.c */
-void rb_iseq_add_mark_object(rb_iseq_t *iseq, VALUE obj);
+void rb_iseq_add_mark_object(const rb_iseq_t *iseq, VALUE obj);
 VALUE rb_iseq_load(VALUE data, VALUE parent, VALUE opt);
 VALUE rb_iseq_parameters(const rb_iseq_t *iseq, int is_proc);
 struct st_table *ruby_insn_make_insn_table(void);