gc.c (clear_error_object): need to mark class of error objects; ref
@@ -1108,6 +1108,7 @@ clear_error_object(mrb_state *mrb, struct RObject *obj)
if (obj == 0) return;
if (!is_white(obj)) return;
paint_black(obj);
+ mrb_gc_mark(mrb, (struct RBasic*)obj->c);
mrb_gc_free_iv(mrb, obj);
struct RException *err = (struct RException*)obj;
err->iv = NULL;
