diff --git a/extlib/benz/gc.c b/extlib/benz/gc.c
index 5d3c5f9d..aedd9836 100644
--- a/extlib/benz/gc.c
+++ b/extlib/benz/gc.c
@@ -375,6 +375,9 @@ gc_mark_object(pic_state *pic, struct pic_object *obj)
       }
     } else {
       gc_mark_object(pic, (struct pic_object *)proc->u.f.name);
+      if (proc->u.f.env) {
+        gc_mark_object(pic, (struct pic_object *)proc->u.f.env);
+      }
     }
     break;
   }
diff --git a/extlib/benz/include/picrin/proc.h b/extlib/benz/include/picrin/proc.h
index eaac2ef7..caa49cc6 100644
--- a/extlib/benz/include/picrin/proc.h
+++ b/extlib/benz/include/picrin/proc.h
@@ -27,6 +27,7 @@ struct pic_proc {
     struct {
       pic_func_t func;
       pic_sym *name;
+      struct pic_dict *env;
     } f;
     struct {
       struct pic_irep *irep;
@@ -48,6 +49,9 @@ struct pic_proc *pic_make_proc(pic_state *, pic_func_t, const char *);
 struct pic_proc *pic_make_proc_irep(pic_state *, struct pic_irep *, struct pic_context *);
 
 pic_sym *pic_proc_name(struct pic_proc *);
+struct pic_dict *pic_proc_env(pic_state *, struct pic_proc *);
+pic_value pic_proc_env_ref(pic_state *, struct pic_proc *, const char *);
+void pic_proc_env_set(pic_state *, struct pic_proc *, const char *, pic_value);
 
 #if defined(__cplusplus)
 }
diff --git a/extlib/benz/proc.c b/extlib/benz/proc.c
index e8c80f7a..d730c909 100644
--- a/extlib/benz/proc.c
+++ b/extlib/benz/proc.c
@@ -18,6 +18,7 @@ pic_make_proc(pic_state *pic, pic_func_t func, const char *name)
   proc->tag = PIC_PROC_TAG_FUNC;
   proc->u.f.func = func;
   proc->u.f.name = sym;
+  proc->u.f.env = NULL;
   return proc;
 }
 
@@ -45,6 +46,29 @@ pic_proc_name(struct pic_proc *proc)
   PIC_UNREACHABLE();
 }
 
+struct pic_dict *
+pic_proc_env(pic_state *pic, struct pic_proc *proc)
+{
+  assert(pic_proc_func_p(proc));
+
+  if (! proc->u.f.env) {
+    proc->u.f.env = pic_make_dict(pic);
+  }
+  return proc->u.f.env;
+}
+
+pic_value
+pic_proc_env_ref(pic_state *pic, struct pic_proc *proc, const char *key)
+{
+  return pic_dict_ref(pic, pic_proc_env(pic, proc), pic_intern_cstr(pic, key));
+}
+
+void
+pic_proc_env_set(pic_state *pic, struct pic_proc *proc, const char *key, pic_value val)
+{
+  pic_dict_set(pic, pic_proc_env(pic, proc), pic_intern_cstr(pic, key), val);
+}
+
 static pic_value
 pic_proc_proc_p(pic_state *pic)
 {