diff --git a/mrbgems/mruby-object-ext/src/object.c b/mrbgems/mruby-object-ext/src/object.c
index 0aeba480e..31cf6e7fd 100644
--- a/mrbgems/mruby-object-ext/src/object.c
+++ b/mrbgems/mruby-object-ext/src/object.c
@@ -97,21 +97,90 @@ obj_instance_exec(mrb_state *mrb, mrb_value self)
   return mrb_object_exec(mrb, self, mrb_singleton_class_ptr(mrb, self));
 }
 
+#ifndef MRB_NO_PRESYM
+#define NIL_EXT_ROM_MT_SIZE 3
+static struct {
+  union mt_ptr vals[NIL_EXT_ROM_MT_SIZE];
+  mrb_sym keys[NIL_EXT_ROM_MT_SIZE];
+} nil_ext_rom_data = {
+  .vals = {
+    { .func = nil_to_a },
+    { .func = nil_to_h },
+    { .func = nil_to_i },
+  },
+  .keys = {
+    MT_KEY(MRB_SYM(to_a), MT_FUNC|MT_NOARG|MT_PUBLIC),
+    MT_KEY(MRB_SYM(to_h), MT_FUNC|MT_NOARG|MT_PUBLIC),
+    MT_KEY(MRB_SYM(to_i), MT_FUNC|MT_NOARG|MT_PUBLIC),
+  }
+};
+static mt_tbl nil_ext_rom_mt = {
+  NIL_EXT_ROM_MT_SIZE, NIL_EXT_ROM_MT_SIZE,
+  (union mt_ptr*)&nil_ext_rom_data, NULL
+};
+
+#define KERNEL_EXT_ROM_MT_SIZE 1
+static struct {
+  union mt_ptr vals[KERNEL_EXT_ROM_MT_SIZE];
+  mrb_sym keys[KERNEL_EXT_ROM_MT_SIZE];
+} kernel_ext_rom_data = {
+  .vals = {
+    { .func = mrb_obj_itself },
+  },
+  .keys = {
+    MT_KEY(MRB_SYM(itself), MT_FUNC|MT_NOARG|MT_PUBLIC),
+  }
+};
+static mt_tbl kernel_ext_rom_mt = {
+  KERNEL_EXT_ROM_MT_SIZE, KERNEL_EXT_ROM_MT_SIZE,
+  (union mt_ptr*)&kernel_ext_rom_data, NULL
+};
+
+#define BOB_EXT_ROM_MT_SIZE 1
+static struct {
+  union mt_ptr vals[BOB_EXT_ROM_MT_SIZE];
+  mrb_sym keys[BOB_EXT_ROM_MT_SIZE];
+} bob_ext_rom_data = {
+  .vals = {
+    { .func = obj_instance_exec },
+  },
+  .keys = {
+    MT_KEY(MRB_SYM(instance_exec), MT_FUNC|MT_PUBLIC),
+  }
+};
+static mt_tbl bob_ext_rom_mt = {
+  BOB_EXT_ROM_MT_SIZE, BOB_EXT_ROM_MT_SIZE,
+  (union mt_ptr*)&bob_ext_rom_data, NULL
+};
+#endif /* !MRB_NO_PRESYM */
+
 void
 mrb_mruby_object_ext_gem_init(mrb_state* mrb)
 {
   struct RClass * n = mrb->nil_class;
 
+#ifndef MRB_NO_PRESYM
+  mrb_mt_init_rom(n, &nil_ext_rom_mt);
+#else
   mrb_define_method_id(mrb, n, MRB_SYM(to_a), nil_to_a,       MRB_ARGS_NONE());
+  mrb_define_method_id(mrb, n, MRB_SYM(to_h), nil_to_h,       MRB_ARGS_NONE());
+  mrb_define_method_id(mrb, n, MRB_SYM(to_i), nil_to_i,       MRB_ARGS_NONE());
+#endif
 #ifndef MRB_NO_FLOAT
   mrb_define_method_id(mrb, n, MRB_SYM(to_f), nil_to_f,       MRB_ARGS_NONE());
 #endif
-  mrb_define_method_id(mrb, n, MRB_SYM(to_h), nil_to_h,       MRB_ARGS_NONE());
-  mrb_define_method_id(mrb, n, MRB_SYM(to_i), nil_to_i,       MRB_ARGS_NONE());
 
+#ifndef MRB_NO_PRESYM
+  mrb_mt_init_rom(mrb->kernel_module, &kernel_ext_rom_mt);
+#else
   mrb_define_method_id(mrb, mrb->kernel_module, MRB_SYM(itself), mrb_obj_itself, MRB_ARGS_NONE());
+#endif
 
+#ifndef MRB_NO_PRESYM
+  mrb_mt_init_rom(mrb_class_get_id(mrb, MRB_SYM(BasicObject)), &bob_ext_rom_mt);
+#else
   mrb_define_method_id(mrb, mrb_class_get_id(mrb, MRB_SYM(BasicObject)), MRB_SYM(instance_exec), obj_instance_exec, MRB_ARGS_ANY() | MRB_ARGS_BLOCK());
+#endif
 }
 
 void