diff --git a/extlib/benz/gc.c b/extlib/benz/gc.c
index 0e4ef903..922968d5 100644
--- a/extlib/benz/gc.c
+++ b/extlib/benz/gc.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/object.h"
 
 union header {
   struct {
diff --git a/extlib/benz/include/picrin.h b/extlib/benz/include/picrin.h
index a73bccd6..47d5b16e 100644
--- a/extlib/benz/include/picrin.h
+++ b/extlib/benz/include/picrin.h
@@ -271,7 +271,6 @@ int pic_str_hash(pic_state *, struct pic_string *);
 #include "picrin/string.h"
 #include "picrin/symbol.h"
 #include "picrin/vector.h"
-#include "picrin/weak.h"
 
 void *pic_default_allocf(void *, void *, size_t);
 
diff --git a/extlib/benz/include/picrin/weak.h b/extlib/benz/include/picrin/object.h
similarity index 87%
rename from extlib/benz/include/picrin/weak.h
rename to extlib/benz/include/picrin/object.h
index 914865b8..bef9590f 100644
--- a/extlib/benz/include/picrin/weak.h
+++ b/extlib/benz/include/picrin/object.h
@@ -2,8 +2,8 @@
  * See Copyright Notice in picrin.h
  */
 
-#ifndef PICRIN_WEAK_H
-#define PICRIN_WEAK_H
+#ifndef PICRIN_OBJECT_H
+#define PICRIN_OBJECT_H
 
 #if defined(__cplusplus)
 extern "C" {
@@ -19,6 +19,7 @@ struct pic_weak {
 
 #define pic_weak_ptr(v) ((struct pic_weak *)pic_obj_ptr(v))
 
+
 #if defined(__cplusplus)
 }
 #endif
diff --git a/extlib/benz/var.c b/extlib/benz/var.c
index 1965db92..5b132a06 100644
--- a/extlib/benz/var.c
+++ b/extlib/benz/var.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/object.h"
 
 static pic_value
 var_get(pic_state *pic, struct pic_proc *var)
diff --git a/extlib/benz/weak.c b/extlib/benz/weak.c
index 484bcbd8..86821dae 100644
--- a/extlib/benz/weak.c
+++ b/extlib/benz/weak.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/object.h"
 
 KHASH_DEFINE(weak, void *, pic_value, kh_ptr_hash_func, kh_ptr_hash_equal)