gistfile1.diff

diff --git a/src/class.c b/src/class.c
index a50d3d8..9080265 100644
--- a/src/class.c
+++ b/src/class.c
@@ -78,8 +78,14 @@ prepare_singleton_class(mrb_state *mrb, struct RBasic *o)
   }
   else if (o->tt == MRB_TT_SCLASS) {
     c = (struct RClass*)o;
-    make_metaclass(mrb, c->super);
-    sc->super = c->super->c;
+    while (c->tt != MRB_TT_CLASS) {
+      c = c->super;
+      if (!c) {
+        mrb_bug(mrb, "corrupted class chain!");
+      }
+    }
+    make_metaclass(mrb, c);
+    sc->super = c->c;
   }
   else {
     sc->super = o->c;