diff --git a/doc/guides/mrbconf.md b/doc/guides/mrbconf.md
index 823a0ba17..a17b84f13 100644
--- a/doc/guides/mrbconf.md
+++ b/doc/guides/mrbconf.md
@@ -236,12 +236,6 @@ end
 - Ignored if `MRB_NO_METHOD_CACHE` is defined.
 - Need to be the power of 2.
 
-`MRB_USE_METHOD_T_STRUCT`
-
-- Use C struct to represent `mrb_method_t`
-- No `MRB_USE_METHOD_T_STRUCT` requires highest 2 bits of function pointers to be zero
-- Define this macro on machines that use higher bits of pointers
-
 `MRB_USE_ALL_SYMBOLS`
 
 - Make it available `Symbol.all_symbols` in `mrbgems/mruby-symbol-ext`
diff --git a/include/mrbconf.h b/include/mrbconf.h
index 122eb2b0e..68ec904f4 100644
--- a/include/mrbconf.h
+++ b/include/mrbconf.h
@@ -48,16 +48,6 @@
 //#define MRB_METHOD_CACHE_SIZE (1<<8)
 //#define MRB_USE_INLINE_METHOD_CACHE
 
-/* add -DMRB_USE_METHOD_T_STRUCT on machines that use higher bits of function pointers */
-/* no MRB_USE_METHOD_T_STRUCT requires highest 2 bits of function pointers to be zero */
-#ifndef MRB_USE_METHOD_T_STRUCT
-  // can't use highest 2 bits of function pointers at least on 32bit
-  // Windows and 32bit Linux.
-# ifdef MRB_32BIT
-#   define MRB_USE_METHOD_T_STRUCT
-# endif
-#endif
-
 /* define on big endian machines; used by MRB_NAN_BOXING, etc. */
 #ifndef MRB_ENDIAN_BIG
 # if (defined(BYTE_ORDER) && defined(BIG_ENDIAN) && BYTE_ORDER == BIG_ENDIAN) || \
@@ -170,9 +160,6 @@
 //#define MRB_USE_ALL_SYMBOLS /* Symbol.all_symbols */
 
 /* obsolete configurations */
-#ifdef MRB_METHOD_T_STRUCT
-# define MRB_USE_METHOD_T_STRUCT
-#endif
 #if defined(DISABLE_STDIO) || defined(MRB_DISABLE_STDIO)
 # define MRB_NO_STDIO
 #endif
diff --git a/include/mruby.h b/include/mruby.h
index a42e0942c..c5cbeca7e 100644
--- a/include/mruby.h
+++ b/include/mruby.h
@@ -230,22 +230,19 @@ mrb_static_assert_powerof2(MRB_METHOD_CACHE_SIZE);
  */
 typedef mrb_value (*mrb_func_t)(struct mrb_state *mrb, mrb_value self);
 
-#ifndef MRB_USE_METHOD_T_STRUCT
-typedef uintptr_t mrb_method_t;
-#else
 typedef struct {
-  uint8_t flags;
+  uint32_t flags;                       /* compatible with mt keys in class.c */
+
   union {
     struct RProc *proc;
     mrb_func_t func;
   };
 } mrb_method_t;
-#endif
 
 #ifndef MRB_NO_METHOD_CACHE
 struct mrb_cache_entry {
   struct RClass *c, *c0;
-  mrb_sym mid;
+  /* mrb_sym mid; // mid is stored in mrb_method_t::flags */
   mrb_method_t m;
 };
 #endif
diff --git a/include/mruby/proc.h b/include/mruby/proc.h
index 22154df8b..f6ee64d93 100644
--- a/include/mruby/proc.h
+++ b/include/mruby/proc.h
@@ -106,20 +106,6 @@ MRB_API mrb_value mrb_proc_cfunc_env_get(mrb_state *mrb, mrb_int idx);
 #define MRB_METHOD_FUNC_FL 1
 #define MRB_METHOD_NOARG_FL 2
 
-#ifndef MRB_USE_METHOD_T_STRUCT
-
-#define MRB_METHOD_FUNC_P(m) (((uintptr_t)(m))&MRB_METHOD_FUNC_FL)
-#define MRB_METHOD_NOARG_P(m) ((((uintptr_t)(m))&MRB_METHOD_NOARG_FL)?1:0)
-#define MRB_METHOD_NOARG_SET(m) ((m)=(mrb_method_t)(((uintptr_t)(m))|MRB_METHOD_NOARG_FL))
-#define MRB_METHOD_FUNC(m) ((mrb_func_t)((uintptr_t)(m)>>2))
-#define MRB_METHOD_FROM_FUNC(m,fn) ((m)=(mrb_method_t)((((uintptr_t)(fn))<<2)|MRB_METHOD_FUNC_FL))
-#define MRB_METHOD_FROM_PROC(m,pr) ((m)=(mrb_method_t)(pr))
-#define MRB_METHOD_PROC_P(m) (!MRB_METHOD_FUNC_P(m))
-#define MRB_METHOD_PROC(m) ((struct RProc*)(m))
-#define MRB_METHOD_UNDEF_P(m) ((m)==0)
-
-#else
-
 #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)
 #define MRB_METHOD_FUNC(m) ((m).func)
@@ -130,8 +116,6 @@ MRB_API mrb_value mrb_proc_cfunc_env_get(mrb_state *mrb, mrb_int idx);
 #define MRB_METHOD_PROC(m) ((m).proc)
 #define MRB_METHOD_UNDEF_P(m) ((m).proc==NULL)
 
-#endif /* MRB_USE_METHOD_T_STRUCT */
-
 #define MRB_METHOD_CFUNC_P(m) (MRB_METHOD_FUNC_P(m)?TRUE:(MRB_METHOD_PROC(m)?(MRB_PROC_CFUNC_P(MRB_METHOD_PROC(m))):FALSE))
 #define MRB_METHOD_CFUNC(m) (MRB_METHOD_FUNC_P(m)?MRB_METHOD_FUNC(m):((MRB_METHOD_PROC(m)&&MRB_PROC_CFUNC_P(MRB_METHOD_PROC(m)))?MRB_PROC_CFUNC(MRB_METHOD_PROC(m)):NULL))
 
diff --git a/src/class.c b/src/class.c
index 1990bd765..4033ccbce 100644
--- a/src/class.c
+++ b/src/class.c
@@ -19,6 +19,8 @@
 #include <mruby/internal.h>
 #include <mruby/presym.h>
 
+#define METHOD_MID(m) MT_KEY_SYM((m).flags)
+
 union mt_ptr {
   struct RProc *proc;
   mrb_func_t func;
@@ -243,17 +245,7 @@ mt_free(mrb_state *mrb, mt_tbl *t)
 static inline mrb_method_t
 create_method_value(mrb_state *mrb, mrb_sym key, union mt_ptr val)
 {
-  mrb_method_t m;
-
-  if (key & MT_FUNC_P) {
-    MRB_METHOD_FROM_FUNC(m, val.func);
-  }
-  else {
-    MRB_METHOD_FROM_PROC(m, val.proc);
-  }
-  if (key & MT_NOARG_P) {
-    MRB_METHOD_NOARG_SET(m);
-  }
+  mrb_method_t m = { key, { val.proc } };
   return m;
 }
 
@@ -795,9 +787,6 @@ mrb_define_method_id(mrb_state *mrb, struct RClass *c, mrb_sym mid, mrb_func_t f
   int ai = mrb_gc_arena_save(mrb);
 
   MRB_METHOD_FROM_FUNC(m, func);
-#ifndef MRB_USE_METHOD_T_STRUCT
-  mrb_assert(MRB_METHOD_FUNC(m) == func);
-#endif
   if (aspec == MRB_ARGS_NONE()) {
     MRB_METHOD_NOARG_SET(m);
   }
@@ -1754,10 +1743,10 @@ mc_clear_by_id(mrb_state *mrb, mrb_sym id)
   struct mrb_cache_entry *mc = mrb->cache;
 
   for (int i=0; i<MRB_METHOD_CACHE_SIZE; mc++,i++) {
-    if (mc->mid == id) mc->c = NULL;
+    if (METHOD_MID(mc->m) == id) mc->c = NULL;
   }
 }
-#endif
+#endif // MRB_NO_METHOD_CACHE
 
 mrb_method_t
 mrb_vm_find_method(mrb_state *mrb, struct RClass *c, struct RClass **cp, mrb_sym mid)
@@ -1768,7 +1757,7 @@ mrb_vm_find_method(mrb_state *mrb, struct RClass *c, struct RClass **cp, mrb_sym
   int h = mrb_int_hash_func(mrb, ((intptr_t)oc) ^ mid) & (MRB_METHOD_CACHE_SIZE-1);
   struct mrb_cache_entry *mc = &mrb->cache[h];
 
-  if (mc->c == c && mc->mid == mid) {
+  if (mc->c == c && METHOD_MID(mc->m) == mid) {
     *cp = mc->c0;
     return mc->m;
   }
@@ -1787,7 +1776,6 @@ mrb_vm_find_method(mrb_state *mrb, struct RClass *c, struct RClass **cp, mrb_sym
 #ifndef MRB_NO_METHOD_CACHE
         mc->c = oc;
         mc->c0 = c;
-        mc->mid = mid;
         mc->m = m;
 #endif
         return m;