diff --git a/include/mruby/proc.h b/include/mruby/proc.h
index 489b4c95e..f6cddf0e5 100644
--- a/include/mruby/proc.h
+++ b/include/mruby/proc.h
@@ -114,6 +114,8 @@ MRB_API mrb_value mrb_proc_cfunc_env_get(mrb_state *mrb, mrb_int idx);
 #define MRB_METHOD_PUBLIC_FL 0
 #define MRB_METHOD_PRIVATE_FL 1
 #define MRB_METHOD_PROTECTED_FL 2
+#define MRB_METHOD_VDEFAULT_FL 3
+#define MRB_METHOD_VISIBILITY_MASK 3
 
 #define MRB_METHOD_FUNC_P(m) ((m).flags&MRB_METHOD_FUNC_FL)
 #define MRB_METHOD_NOARG_P(m) (((m).flags&MRB_METHOD_NOARG_FL)?1:0)
@@ -124,6 +126,8 @@ MRB_API mrb_value mrb_proc_cfunc_env_get(mrb_state *mrb, mrb_int idx);
 #define MRB_METHOD_PROC_P(m) (!MRB_METHOD_FUNC_P(m))
 #define MRB_METHOD_PROC(m) ((m).as.proc)
 #define MRB_METHOD_UNDEF_P(m) ((m).as.proc==NULL)
+#define MRB_METHOD_VISIBILITY(m) ((m).flags & MRB_METHOD_VISIBILITY_MASK)
+#define MRB_METHOD_SET_VISIBILITY(m,v) ((m).flags=(((m).flags&~MRB_METHOD_VISIBILITY_MASK)|(v)))
 
 #define MRB_METHOD_CFUNC_P(m) (MRB_METHOD_FUNC_P(m) || (MRB_METHOD_PROC(m)?(MRB_PROC_CFUNC_P(MRB_METHOD_PROC(m))):FALSE))
 /* use MRB_METHOD_CFUNC(m) only when MRB_METHOD_CFUNC_P(m) is true */
diff --git a/src/class.c b/src/class.c
index e71fe6d4a..65b00c48d 100644
--- a/src/class.c
+++ b/src/class.c
@@ -34,7 +34,8 @@ union mt_ptr {
 #define MT_PUBLIC MRB_METHOD_PUBLIC_FL
 #define MT_PRIVATE MRB_METHOD_PRIVATE_FL
 #define MT_PROTECTED MRB_METHOD_PROTECTED_FL
-#define MT_VMASK 3
+#define MT_VDEFAULT MRB_METHOD_VDEFAULT_FL
+#define MT_VMASK MRB_METHOD_VISIBILITY_MASK
 #define MT_EMPTY 0
 #define MT_DELETED 1
 
@@ -2302,12 +2303,14 @@ mrb_alias_method(mrb_state *mrb, struct RClass *c, mrb_sym a, mrb_sym b)
     const struct RProc *p = MRB_METHOD_PROC(m);
     if (!MRB_PROC_CFUNC_P(p) && !MRB_PROC_ALIAS_P(p)) {
       struct RProc *pnew = MRB_OBJ_ALLOC(mrb, MRB_TT_PROC, mrb->proc_class);
+      int vis = MRB_METHOD_VISIBILITY(m);
 
       pnew->body.mid = b;
       pnew->upper = p;
       pnew->e.env = NULL;
       pnew->flags |= MRB_PROC_ALIAS;
       MRB_METHOD_FROM_PROC(m, pnew);
+      MRB_METHOD_SET_VISIBILITY(m,vis);
     }
   }
   mrb_define_method_raw(mrb, c, a, m);