diff --git a/src/class.c b/src/class.c
index f70dfa7d3..4a32ab986 100644
--- a/src/class.c
+++ b/src/class.c
@@ -3037,6 +3037,8 @@ mrb_init_class(mrb_state *mrb)
   mrb_define_method_id(mrb, bob, MRB_SYM_Q(equal),                         mrb_obj_equal_m,          MRB_ARGS_REQ(1)); /* 15.3.1.3.11 */
   mrb_define_method_id(mrb, bob, MRB_SYM(instance_eval),                   mrb_obj_instance_eval,    MRB_ARGS_OPT(1)|MRB_ARGS_BLOCK());  /* 15.3.1.3.18 */
   mrb_define_private_method_id(mrb, bob, MRB_SYM(singleton_method_added),  mrb_do_nothing,           MRB_ARGS_REQ(1));
+  mrb_define_private_method_id(mrb, bob, MRB_SYM(singleton_method_removed),mrb_do_nothing,           MRB_ARGS_REQ(1));
+  mrb_define_private_method_id(mrb, bob, MRB_SYM(singleton_method_undefined),mrb_do_nothing,         MRB_ARGS_REQ(1));
   mrb_define_private_method_id(mrb, bob, MRB_SYM(method_missing),          mrb_obj_missing,          MRB_ARGS_ANY());  /* 15.3.1.3.30 */
 
   mrb_define_class_method_id(mrb, cls, MRB_SYM(new),                       mrb_class_new_class,      MRB_ARGS_OPT(1)|MRB_ARGS_BLOCK());