diff --git a/compile.c b/compile.c
index 0fefbfeb71..5293b32695 100644
--- a/compile.c
+++ b/compile.c
@@ -9582,15 +9582,29 @@ ibf_load_iseq(const struct ibf_load *load, const rb_iseq_t *index_iseq)
 	}
 	else {
 	    rb_iseq_t *iseq = iseq_imemo_alloc();
+#if IBF_ISEQ_DEBUG
+	    fprintf(stderr, "ibf_load_iseq: new iseq=%p\n", iseq);
+#endif
 	    FL_SET(iseq, ISEQ_NOT_LOADED_YET);
 	    iseq->aux.loader.obj = load->loader_obj;
 	    iseq->aux.loader.index = iseq_index;
+#if IBF_ISEQ_DEBUG
+	    fprintf(stderr, "ibf_load_iseq: iseq=%p loader_obj=%p index=%d\n",
+		    iseq, (void *)load->loader_obj, iseq_index);
+#endif
 	    rb_ary_store(load->iseq_list, iseq_index, (VALUE)iseq);
 
 #if !USE_LAZY_LOAD
+#if IBF_ISEQ_DEBUG
+	    fprintf(stderr, "ibf_load_iseq: loading iseq=%p\n", iseq);
+#endif
 	    ibf_load_iseq_complete(iseq);
 #endif /* !USE_LAZY_LOAD */
 
+#if IBF_ISEQ_DEBUG
+	    fprintf(stderr, "ibf_load_iseq: iseq=%p loaded %p\n",
+		    iseq, load->iseq);
+#endif
 	    if (load->iseq) {
 		iseq_add_mark_object(load->iseq, (VALUE)iseq);
 	    }