diff --git a/include/picrin/proc.h b/include/picrin/proc.h
index 21a24b21..89d06163 100644
--- a/include/picrin/proc.h
+++ b/include/picrin/proc.h
@@ -29,4 +29,10 @@ struct pic_proc {
 struct pic_proc *pic_proc_new(pic_state *, pic_func_t);
 struct pic_proc *pic_proc_new_irep(pic_state *, struct pic_irep *, struct pic_env *);
 
+/* closed variables accessor */
+void pic_proc_cv_reserve(pic_state *, struct pic_proc *, size_t);
+int pic_proc_cv_size(pic_state *, struct pic_proc *);
+pic_value pic_proc_cv_ref(pic_state *, struct pic_proc *, size_t);
+void pic_proc_cv_set(pic_state *, struct pic_proc *, size_t, pic_value);
+
 #endif
diff --git a/src/cont.c b/src/cont.c
index 63e856ff..ec5d311c 100644
--- a/src/cont.c
+++ b/src/cont.c
@@ -164,11 +164,8 @@ pic_cont_callcc(pic_state *pic)
     c = pic_proc_new(pic, cont_call);
 
     /* save the continuation object in proc */
-    c->env = (struct pic_env *)pic_obj_alloc(pic, sizeof(struct pic_env), PIC_TT_ENV);
-    c->env->up = NULL;
-    c->env->valuec = 1;
-    c->env->values = (pic_value *)pic_calloc(pic, 1, sizeof(pic_value));
-    c->env->values[0] = pic_obj_value(cont);
+    pic_proc_cv_reserve(pic, c, 1);
+    pic_proc_cv_set(pic, c, 0, pic_obj_value(cont));
 
     return pic_apply_argv(pic, cb, 1, pic_obj_value(c));
   }
diff --git a/src/proc.c b/src/proc.c
index 759b0446..6f772de8 100644
--- a/src/proc.c
+++ b/src/proc.c
@@ -27,6 +27,46 @@ pic_proc_new_irep(pic_state *pic, struct pic_irep *irep, struct pic_env *env)
   return proc;
 }
 
+void
+pic_proc_cv_reserve(pic_state *pic, struct pic_proc *proc, size_t cv_size)
+{
+  struct pic_env *env;
+
+  if (proc->env != NULL) {
+    pic_error(pic, "env slot already in use");
+  }
+  env = (struct pic_env *)pic_obj_alloc(pic, sizeof(struct pic_env), PIC_TT_ENV);
+  env->valuec = cv_size;
+  env->values = (pic_value *)pic_calloc(pic, cv_size, sizeof(pic_value));
+  env->up = NULL;
+
+  proc->env = env;
+}
+
+int
+pic_proc_cv_size(pic_state *pic, struct pic_proc *proc)
+{
+  return proc->env ? proc->env->valuec : 0;
+}
+
+pic_value
+pic_proc_cv_ref(pic_state *pic, struct pic_proc *proc, size_t i)
+{
+  if (proc->env == NULL) {
+    pic_error(pic, "no closed env");
+  }
+  return proc->env->values[i];
+}
+
+void
+pic_proc_cv_set(pic_state *pic, struct pic_proc *proc, size_t i, pic_value v)
+{
+  if (proc->env == NULL) {
+    pic_error(pic, "no closed env");
+  }
+  proc->env->values[i] = v;
+}
+
 static pic_value
 pic_proc_proc_p(pic_state *pic)
 {