diff --git a/include/picrin/proc.h b/include/picrin/proc.h
index c29b6c36..b51b9a53 100644
--- a/include/picrin/proc.h
+++ b/include/picrin/proc.h
@@ -4,7 +4,7 @@
 struct pic_env {
   PIC_OBJECT_HEADER
   pic_value *values;
-  int numcv;
+  int num_val;
   struct pic_env *up;
 };
 
diff --git a/src/gc.c b/src/gc.c
index 13e5ecb8..48e2b3ca 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -163,7 +163,7 @@ gc_mark_object(pic_state *pic, struct pic_object *obj)
     struct pic_env *env = (struct pic_env *)obj;
     int i;
 
-    for (i = 0; i < env->numcv; ++i) {
+    for (i = 0; i < env->num_val; ++i) {
       gc_mark(pic, env->values[i]);
     }
     gc_mark_object(pic, (struct pic_object *)env->up);
diff --git a/src/vm.c b/src/vm.c
index 1e2bb2b3..ae8494ee 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -280,8 +280,8 @@ pic_run(pic_state *pic, struct pic_proc *proc, pic_value args)
       struct pic_env *env;
 
       env = (struct pic_env *)pic_obj_alloc(pic, sizeof(struct pic_env), PIC_TT_ENV);
-      env->numcv = pic->irep[pc->u.i]->argc;
-      env->values = (pic_value *)pic_alloc(pic, sizeof(pic_value) * env->numcv);
+      env->num_val = pic->irep[pc->u.i]->argc;
+      env->values = (pic_value *)pic_alloc(pic, sizeof(pic_value) * env->num_val);
       env->up = pic_proc_ptr(*pic->ci->fp)->env;
 
       proc = pic_proc_new(pic, pic->irep[pc->u.i], env);