diff --git a/src/array.c b/src/array.c
index f87e36479..815c67f28 100644
--- a/src/array.c
+++ b/src/array.c
@@ -1913,7 +1913,7 @@ mrb_init_array(mrb_state *mrb)
   mrb_define_method_id(mrb, a, MRB_SYM(first),           mrb_ary_first,        MRB_ARGS_OPT(1));   /* 15.2.12.5.13 */
   mrb_define_method_id(mrb, a, MRB_SYM(index),           mrb_ary_index_m,      MRB_ARGS_REQ(1));   /* 15.2.12.5.14 */
   mrb_define_method_id(mrb, a, MRB_SYM(initialize),      mrb_ary_init,         MRB_ARGS_OPT(2));   /* 15.2.12.5.15 */
-  mrb_define_method_id(mrb, a, MRB_SYM(initialize_copy), mrb_ary_replace_m,    MRB_ARGS_REQ(1));   /* 15.2.12.5.16 */
+  mrb_define_private_method_id(mrb, a, MRB_SYM(initialize_copy), mrb_ary_replace_m, MRB_ARGS_REQ(1)); /* 15.2.12.5.16 */
   mrb_define_method_id(mrb, a, MRB_SYM(join),            mrb_ary_join_m,       MRB_ARGS_OPT(1));   /* 15.2.12.5.17 */
   mrb_define_method_id(mrb, a, MRB_SYM(last),            mrb_ary_last,         MRB_ARGS_OPT(1));   /* 15.2.12.5.18 */
   mrb_define_method_id(mrb, a, MRB_SYM(length),          mrb_ary_size,         MRB_ARGS_NONE());   /* 15.2.12.5.19 */