diff --git a/mrbgems/mruby-pack/src/pack.c b/mrbgems/mruby-pack/src/pack.c
index fa2c227f5..47ad3d85a 100644
--- a/mrbgems/mruby-pack/src/pack.c
+++ b/mrbgems/mruby-pack/src/pack.c
@@ -1390,7 +1390,7 @@ mrb_pack_pack(mrb_state *mrb, mrb_value ary)
 
       o = mrb_ary_ref(mrb, ary, aidx);
       if (type == PACK_TYPE_INTEGER) {
-        o = mrb_to_integer(mrb, o);
+        o = mrb_ensure_int_type(mrb, o);
       }
 #ifndef MRB_NO_FLOAT
       else if (type == PACK_TYPE_FLOAT) {