diff --git a/src/gc.c b/src/gc.c
index cd885f7e8..56d316b0d 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -647,7 +647,7 @@ gc_mark_children(mrb_state *mrb, mrb_gc *gc, struct RBasic *obj)
 
       mrb_gc_mark(mrb, (struct RBasic*)p->env);
       mrb_gc_mark(mrb, (struct RBasic*)p->target_class);
-      if (!MRB_PROC_CFUNC_P(p)) {
+      if (!MRB_PROC_CFUNC_P(p) && p->body.irep) {
         mrb_gc_mark(mrb, (struct RBasic*)p->body.irep->outer);
       }
     }