diff --git a/src/class.c b/src/class.c
index 184036a91..521423f37 100644
--- a/src/class.c
+++ b/src/class.c
@@ -97,6 +97,7 @@ prepare_singleton_class(mrb_state *mrb, struct RBasic *o)
   }
   else {
     sc->super = o->c;
+    prepare_singleton_class(mrb, (struct RBasic*)sc);
   }
   o->c = sc;
   mrb_field_write_barrier(mrb, (struct RBasic*)o, (struct RBasic*)sc);