diff --git a/include/mruby/value.h b/include/mruby/value.h
index 60c018ab4..c9a735611 100644
--- a/include/mruby/value.h
+++ b/include/mruby/value.h
@@ -164,7 +164,7 @@ static const unsigned int IEEE754_INFINITY_BITS_SINGLE = 0x7F800000;
   f(MRB_TT_RATIONAL,    struct RRational,   "Rational") \
   f(MRB_TT_BIGINT,      struct RBigint,     "Integer") \
   f(MRB_TT_BACKTRACE,   struct RBacktrace,  "backtrace") \
-  f(MRB_TT_SET,         struct RData,       "Set")
+  f(MRB_TT_SET,         struct RSet,        "Set")
 
 enum mrb_vtype {
 #define MRB_VTYPE_DEFINE(tt, type, name) tt,
diff --git a/mrbgems/mruby-set/src/set.c b/mrbgems/mruby-set/src/set.c
index f64df6fc6..5e08eacc3 100644
--- a/mrbgems/mruby-set/src/set.c
+++ b/mrbgems/mruby-set/src/set.c
@@ -19,6 +19,11 @@
 KHASH_DECLARE(set, mrb_value, char, FALSE)
 KHASH_DEFINE(set, mrb_value, char, FALSE, mrb_obj_hash_code, mrb_eql)
 
+struct RSet {
+  MRB_OBJECT_HEADER;
+  khash_t(set) *kh;
+};
+
 static void
 set_copy_elements(mrb_state *mrb, khash_t(set) *target_kh, khash_t(set) *source_kh)
 {
@@ -31,48 +36,28 @@ set_copy_elements(mrb_state *mrb, khash_t(set) *target_kh, khash_t(set) *source_
   }
 }
 
-#define SET_KHASH_IV MRB_SYM(khash)
-
-static void
-set_free(mrb_state *mrb, void *ptr)
-{
-  khash_t(set) *kh = (khash_t(set)*)ptr;
-  if (kh) {
-    kh_destroy(set, mrb, kh);
-  }
-}
-
-static const struct mrb_data_type set_data_type = {
-  "Set", set_free
-};
-
+#define mrb_set_ptr(o) ((struct RSet*)mrb_obj_ptr(o))
 static void
 set_set_khash(mrb_state *mrb, mrb_value self, khash_t(set) *kh)
 {
-  /* When MRB_TT_SET is used, RData's type field is not strictly necessary */
-  /* for type checking if mrb_type() is MRB_TT_SET. However, it can still hold */
-  /* the dfree function if we choose to use it via a generic RData path. */
-  /* For now, keeping it for set_free via set_data_type if needed. */
-  ((struct RData*)mrb_obj_ptr(self))->type = &set_data_type;
-  ((struct RData*)mrb_obj_ptr(self))->data = kh;
+  mrb_check_type(mrb, self, MRB_TT_SET);
+  struct RSet *set = mrb_set_ptr(self);
+  set->kh = kh;
 }
 
 static khash_t(set) *
 set_get_khash(mrb_state *mrb, mrb_value self)
 {
-  mrb_assert(mrb_type(self) == MRB_TT_SET);
-  return (khash_t(set)*)((struct RData*)mrb_obj_ptr(self))->data;
+  mrb_check_type(mrb, self, MRB_TT_SET);
+  return mrb_set_ptr(self)->kh;
 }
 
-#ifdef MRB_USE_SET
 /* Mark function for Set instances */
 size_t
 mrb_gc_mark_set(mrb_state *mrb, struct RBasic *obj)
 {
-  struct RData *d = (struct RData*)obj;
-  if (!d->data) return 0;
-
-  khash_t(set) *kh = (khash_t(set)*)d->data;
+  struct RSet *s = (struct RSet*)obj;
+  khash_t(set) *kh = s->kh;
   if (!kh) return 0;
 
   KHASH_FOREACH(mrb, kh, k) {
@@ -86,16 +71,14 @@ mrb_gc_mark_set(mrb_state *mrb, struct RBasic *obj)
 void
 mrb_gc_free_set(mrb_state *mrb, struct RBasic *obj)
 {
-  struct RData *d = (struct RData*)obj;
-  if (d->data) {
-    khash_t(set) *kh = (khash_t(set)*)d->data;
+  struct RSet *s = (struct RSet*)obj;
+  if (s->kh) {
+    khash_t(set) *kh = s->kh;
     if (kh) {
       kh_destroy(set, mrb, kh);
     }
   }
-  mrb_gc_free_iv(mrb, (struct RObject*)obj);
 }
-#endif
 
 /* Helper function to check if a value is a Set and return a boolean result */
 static mrb_bool