diff --git a/include/mruby/value.h b/include/mruby/value.h
index a48dcb7ab..860f6f894 100644
--- a/include/mruby/value.h
+++ b/include/mruby/value.h
@@ -152,7 +152,7 @@ static const unsigned int IEEE754_INFINITY_BITS_SINGLE = 0x7F800000;
   f(MRB_TT_RANGE,       struct RRange,      "Range") \
   f(MRB_TT_EXCEPTION,   struct RException,  "Exception") \
   f(MRB_TT_ENV,         struct REnv,        "env") \
-  f(MRB_TT_DATA,        struct RData,       "Data") \
+  f(MRB_TT_CDATA,       struct RData,       "C data") \
   f(MRB_TT_FIBER,       struct RFiber,      "Fiber") \
   f(MRB_TT_STRUCT,      struct RArray,      "Struct") \
   f(MRB_TT_ISTRUCT,     struct RIStruct,    "istruct") \
@@ -168,6 +168,9 @@ enum mrb_vtype {
   MRB_TT_MAXDEFINE
 };
 
+/* obsolete name for MRB_TT_CDATA */
+#define MRB_TT_DATA MRB_TT_CDATA
+
 #define MRB_VTYPE_TYPEOF(tt) MRB_TYPEOF_##tt
 
 #define MRB_VTYPE_TYPEDEF(tt, type, name) typedef type MRB_VTYPE_TYPEOF(tt);
@@ -290,7 +293,7 @@ struct RCptr {
 #define mrb_env_p(o) (mrb_type(o) == MRB_TT_ENV)
 #endif
 #ifndef mrb_data_p
-#define mrb_data_p(o) (mrb_type(o) == MRB_TT_DATA)
+#define mrb_data_p(o) (mrb_type(o) == MRB_TT_CDATA)
 #endif
 #ifndef mrb_fiber_p
 #define mrb_fiber_p(o) (mrb_type(o) == MRB_TT_FIBER)
diff --git a/mrbgems/mruby-io/src/file.c b/mrbgems/mruby-io/src/file.c
index 73de3e78c..e0957ffa6 100644
--- a/mrbgems/mruby-io/src/file.c
+++ b/mrbgems/mruby-io/src/file.c
@@ -594,7 +594,7 @@ mrb_init_file(mrb_state *mrb)
 
   io   = mrb_class_get_id(mrb, MRB_SYM(IO));
   file = mrb_define_class(mrb, "File", io);
-  MRB_SET_INSTANCE_TT(file, MRB_TT_DATA);
+  MRB_SET_INSTANCE_TT(file, MRB_TT_CDATA);
   mrb_define_class_method(mrb, file, "umask",  mrb_file_s_umask, MRB_ARGS_OPT(1));
   mrb_define_class_method(mrb, file, "delete", mrb_file_s_unlink, MRB_ARGS_ANY());
   mrb_define_class_method(mrb, file, "unlink", mrb_file_s_unlink, MRB_ARGS_ANY());
diff --git a/mrbgems/mruby-io/src/io.c b/mrbgems/mruby-io/src/io.c
index e4c96e167..51dd87750 100644
--- a/mrbgems/mruby-io/src/io.c
+++ b/mrbgems/mruby-io/src/io.c
@@ -331,7 +331,7 @@ option_to_fd(mrb_state *mrb, mrb_value v)
   if (mrb_nil_p(v)) return -1;
 
   switch (mrb_type(v)) {
-    case MRB_TT_DATA: /* IO */
+    case MRB_TT_CDATA: /* IO */
       return mrb_io_fileno(mrb, v);
     case MRB_TT_INTEGER:
       return (int)mrb_integer(v);
@@ -1537,7 +1537,7 @@ mrb_init_io(mrb_state *mrb)
   struct RClass *io;
 
   io      = mrb_define_class(mrb, "IO", mrb->object_class);
-  MRB_SET_INSTANCE_TT(io, MRB_TT_DATA);
+  MRB_SET_INSTANCE_TT(io, MRB_TT_CDATA);
 
   mrb_include_module(mrb, io, mrb_module_get(mrb, "Enumerable")); /* 15.2.20.3 */
   mrb_define_class_method(mrb, io, "_popen",  mrb_io_s_popen,   MRB_ARGS_ARG(1,2));
diff --git a/mrbgems/mruby-os-memsize/src/memsize.c b/mrbgems/mruby-os-memsize/src/memsize.c
index c35a38006..b95515cc6 100644
--- a/mrbgems/mruby-os-memsize/src/memsize.c
+++ b/mrbgems/mruby-os-memsize/src/memsize.c
@@ -150,7 +150,7 @@ os_memsize_of_object(mrb_state* mrb, mrb_value obj)
       size += mrb_bint_memsize(obj);
       /* fall through */
 #endif
-    case MRB_TT_DATA:
+    case MRB_TT_CDATA:
     case MRB_TT_ISTRUCT:
       size += mrb_objspace_page_slot_size();
       break;
diff --git a/mrbgems/mruby-time/src/time.c b/mrbgems/mruby-time/src/time.c
index b864e568e..63a9d252f 100644
--- a/mrbgems/mruby-time/src/time.c
+++ b/mrbgems/mruby-time/src/time.c
@@ -1021,7 +1021,7 @@ mrb_mruby_time_gem_init(mrb_state* mrb)
   struct RClass *tc;
   /* ISO 15.2.19.2 */
   tc = mrb_define_class(mrb, "Time", mrb->object_class);
-  MRB_SET_INSTANCE_TT(tc, MRB_TT_DATA);
+  MRB_SET_INSTANCE_TT(tc, MRB_TT_CDATA);
   mrb_include_module(mrb, tc, mrb_module_get(mrb, "Comparable"));
   mrb_define_class_method(mrb, tc, "at", mrb_time_at_m, MRB_ARGS_ARG(1, 1));      /* 15.2.19.6.1 */
   mrb_define_class_method(mrb, tc, "gm", mrb_time_gm, MRB_ARGS_ARG(1,6));       /* 15.2.19.6.2 */
diff --git a/src/class.c b/src/class.c
index 12140f713..8afd792f5 100644
--- a/src/class.c
+++ b/src/class.c
@@ -2749,7 +2749,7 @@ init_copy(mrb_state *mrb, mrb_value dest, mrb_value obj)
     case MRB_TT_OBJECT:
     case MRB_TT_SCLASS:
     case MRB_TT_HASH:
-    case MRB_TT_DATA:
+    case MRB_TT_CDATA:
     case MRB_TT_EXCEPTION:
       mrb_iv_copy(mrb, dest, obj);
       break;
diff --git a/src/etc.c b/src/etc.c
index 28bfdbf8e..834192238 100644
--- a/src/etc.c
+++ b/src/etc.c
@@ -16,7 +16,7 @@ mrb_data_object_alloc(mrb_state *mrb, struct RClass *klass, void *ptr, const mrb
 {
   struct RData *data;
 
-  data = MRB_OBJ_ALLOC(mrb, MRB_TT_DATA, klass);
+  data = MRB_OBJ_ALLOC(mrb, MRB_TT_CDATA, klass);
   data->data = ptr;
   data->type = type;
 
@@ -27,7 +27,7 @@ MRB_API void
 mrb_data_check_type(mrb_state *mrb, mrb_value obj, const mrb_data_type *type)
 {
   if (!mrb_data_p(obj)) {
-    mrb_check_type(mrb, obj, MRB_TT_DATA);
+    mrb_check_type(mrb, obj, MRB_TT_CDATA);
   }
   if (DATA_TYPE(obj) != type) {
     const mrb_data_type *t2 = DATA_TYPE(obj);
@@ -137,7 +137,7 @@ mrb_obj_id(mrb_value obj)
   case MRB_TT_HASH:
   case MRB_TT_RANGE:
   case MRB_TT_EXCEPTION:
-  case MRB_TT_DATA:
+  case MRB_TT_CDATA:
   case MRB_TT_ISTRUCT:
   default:
     return MakeID(mrb_ptr(obj), tt);
diff --git a/src/gc.c b/src/gc.c
index 744f02bbb..923aaf0ec 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -696,7 +696,7 @@ gc_mark_children(mrb_state *mrb, mrb_gc *gc, struct RBasic *obj)
     /* fall through */
 
   case MRB_TT_OBJECT:
-  case MRB_TT_DATA:
+  case MRB_TT_CDATA:
     mrb_gc_mark_iv(mrb, (struct RObject*)obj);
     break;
 
@@ -891,7 +891,7 @@ obj_free(mrb_state *mrb, struct RBasic *obj, int end)
     mrb_gc_free_range(mrb, ((struct RRange*)obj));
     break;
 
-  case MRB_TT_DATA:
+  case MRB_TT_CDATA:
     {
       struct RData *d = (struct RData*)obj;
       if (d->type && d->type->dfree) {
@@ -1010,7 +1010,7 @@ gc_gray_counts(mrb_state *mrb, mrb_gc *gc, struct RBasic *obj)
     break;
 
   case MRB_TT_OBJECT:
-  case MRB_TT_DATA:
+  case MRB_TT_CDATA:
     children += mrb_gc_mark_iv_size(mrb, (struct RObject*)obj);
     break;
 
diff --git a/src/object.c b/src/object.c
index 0b72c21d7..8fc5d3805 100644
--- a/src/object.c
+++ b/src/object.c
@@ -378,7 +378,7 @@ mrb_type_convert_check(mrb_state *mrb, mrb_value val, enum mrb_vtype type, mrb_s
 {
   mrb_value v;
 
-  if (mrb_type(val) == type && type != MRB_TT_DATA && type != MRB_TT_ISTRUCT) return val;
+  if (mrb_type(val) == type && type != MRB_TT_CDATA && type != MRB_TT_ISTRUCT) return val;
   v = convert_type(mrb, val, type_name(type), method, FALSE);
   if (mrb_nil_p(v) || mrb_type(v) != type) return mrb_nil_value();
   return v;
diff --git a/src/variable.c b/src/variable.c
index ea7301770..be27f0eda 100644
--- a/src/variable.c
+++ b/src/variable.c
@@ -300,7 +300,7 @@ obj_iv_p(mrb_value obj)
     case MRB_TT_MODULE:
     case MRB_TT_SCLASS:
     case MRB_TT_HASH:
-    case MRB_TT_DATA:
+    case MRB_TT_CDATA:
     case MRB_TT_EXCEPTION:
       return TRUE;
     default: