diff --git a/mrbgems/mruby-struct/src/struct.c b/mrbgems/mruby-struct/src/struct.c
index fe7e73f04..b567a00d5 100644
--- a/mrbgems/mruby-struct/src/struct.c
+++ b/mrbgems/mruby-struct/src/struct.c
@@ -302,17 +302,19 @@ mrb_struct_s_def(mrb_state *mrb, mrb_value klass)
       }
     }
     rest = mrb_ary_new_from_values(mrb, argcnt, pargv);
-    for (i=0; i<RARRAY_LEN(rest); i++) {
+    for (i=0; i<argcnt; i++) {
       id = mrb_obj_to_sym(mrb, RARRAY_PTR(rest)[i]);
       mrb_ary_set(mrb, rest, i, mrb_symbol_value(id));
     }
-  }
-  st = make_struct(mrb, name, rest, mrb_class_ptr(klass));
-  if (!mrb_nil_p(b)) {
-    mrb_yield_with_class(mrb, b, 1, &st, st, mrb_class_ptr(st));
-  }
+    st = make_struct(mrb, name, rest, mrb_class_ptr(klass));
+    if (!mrb_nil_p(b)) {
+      mrb_yield_with_class(mrb, b, 1, &st, st, mrb_class_ptr(st));
+    }
 
-  return st;
+    return st;
+  }
+  /* not reached */
+  return mrb_nil_value();
 }
 
 static mrb_int