diff --git a/compile.c b/compile.c
index 315e2dc92e..c3b9f5463e 100644
--- a/compile.c
+++ b/compile.c
@@ -562,15 +562,6 @@ APPEND_ELEM(ISEQ_ARG_DECLARE LINK_ANCHOR *const anchor, LINK_ELEMENT *before, LI
 #define APPEND_ELEM(anchor, before, elem) APPEND_ELEM(iseq, (anchor), (before), (elem))
 #endif
 
-static int
-iseq_add_mark_object(const rb_iseq_t *iseq, VALUE v)
-{
-    if (!SPECIAL_CONST_P(v)) {
-	rb_iseq_add_mark_object(iseq, v);
-    }
-    return COMPILE_OK;
-}
-
 static int
 iseq_add_mark_object_compile_time(const rb_iseq_t *iseq, VALUE v)
 {
@@ -749,6 +740,7 @@ rb_iseq_translate_threaded_code(rb_iseq_t *iseq)
 	encoded[i] = (VALUE)table[insn];
 	i += len;
     }
+    FL_SET(iseq, ISEQ_TRANSLATED);
 #endif
     return COMPILE_OK;
 }
@@ -1235,7 +1227,7 @@ new_child_iseq(rb_iseq_t *iseq, const NODE *const node,
 				    rb_iseq_path(iseq), rb_iseq_realpath(iseq),
 				    INT2FIX(line_no), parent, type, ISEQ_COMPILE_DATA(iseq)->option);
     debugs("[new_child_iseq]< ---------------------------------------\n");
-    iseq_add_mark_object(iseq, (VALUE)ret_iseq);
+    iseq_add_mark_object_compile_time(iseq, (VALUE)ret_iseq);
     return ret_iseq;
 }
 
@@ -1250,7 +1242,7 @@ new_child_iseq_ifunc(rb_iseq_t *iseq, const struct vm_ifunc *ifunc,
 				 rb_iseq_path(iseq), rb_iseq_realpath(iseq),
 				 INT2FIX(line_no), parent, type, ISEQ_COMPILE_DATA(iseq)->option);
     debugs("[new_child_iseq_ifunc]< ---------------------------------------\n");
-    iseq_add_mark_object(iseq, (VALUE)ret_iseq);
+    iseq_add_mark_object_compile_time(iseq, (VALUE)ret_iseq);
     return ret_iseq;
 }
 
@@ -1501,7 +1493,6 @@ iseq_set_arguments_keywords(rb_iseq_t *iseq, LINK_ANCHOR *const optargs,
 	    switch (nd_type(val_node)) {
 	      case NODE_LIT:
 		dv = val_node->nd_lit;
-		iseq_add_mark_object(iseq, dv);
 		break;
 	      case NODE_NIL:
 		dv = Qnil;
@@ -2027,6 +2018,7 @@ iseq_set_sequence(rb_iseq_t *iseq, LINK_ANCHOR *const anchor)
 			    rb_hash_rehash(map);
 			    freeze_hide_obj(map);
 			    generated_iseq[code_index + 1 + j] = map;
+			    FL_SET(iseq, ISEQ_MARKABLE_ISEQ);
 			    break;
 			}
 		      case TS_LINDEX:
@@ -2037,6 +2029,9 @@ iseq_set_sequence(rb_iseq_t *iseq, LINK_ANCHOR *const anchor)
 			{
 			    VALUE v = operands[j];
 			    generated_iseq[code_index + 1 + j] = v;
+			    if (!SPECIAL_CONST_P(v)) {
+				FL_SET(iseq, ISEQ_MARKABLE_ISEQ);
+			    }
 			    break;
 			}
 		      case TS_VALUE:	/* VALUE */
@@ -2044,7 +2039,9 @@ iseq_set_sequence(rb_iseq_t *iseq, LINK_ANCHOR *const anchor)
 			    VALUE v = operands[j];
 			    generated_iseq[code_index + 1 + j] = v;
 			    /* to mark ruby object */
-			    iseq_add_mark_object(iseq, v);
+			    if (!SPECIAL_CONST_P(v)) {
+				FL_SET(iseq, ISEQ_MARKABLE_ISEQ);
+			    }
 			    break;
 			}
 		      case TS_IC: /* inline cache */
@@ -2057,6 +2054,17 @@ iseq_set_sequence(rb_iseq_t *iseq, LINK_ANCHOR *const anchor)
 			    generated_iseq[code_index + 1 + j] = (VALUE)ic;
 			    break;
 			}
+		      case TS_ISE: /* inline storage entry */
+			{
+			    unsigned int ic_index = FIX2UINT(operands[j]);
+			    IC ic = (IC)&iseq->body->is_entries[ic_index];
+			    if (UNLIKELY(ic_index >= iseq->body->is_size)) {
+				rb_bug("iseq_set_sequence: ic_index overflow: index: %d, size: %d", ic_index, iseq->body->is_size);
+			    }
+			    generated_iseq[code_index + 1 + j] = (VALUE)ic;
+			    FL_SET(iseq, ISEQ_MARKABLE_ISEQ);
+			    break;
+			}
 		      case TS_CALLINFO: /* call info */
 			{
 			    struct rb_call_info *base_ci = (struct rb_call_info *)operands[j];
@@ -2209,11 +2217,6 @@ iseq_set_exception_table(rb_iseq_t *iseq)
 	    entry->end = label_get_position((LABEL *)(ptr[2] & ~1));
 	    entry->iseq = (rb_iseq_t *)ptr[3];
 
-	    /* register iseq as mark object */
-	    if (entry->iseq != 0) {
-		iseq_add_mark_object(iseq, (VALUE)entry->iseq);
-	    }
-
 	    /* stack depth */
 	    if (ptr[4]) {
 		LABEL *lobj = (LABEL *)(ptr[4] & ~1);
@@ -4808,7 +4811,7 @@ compile_case(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const orig_nod
     }
 
     if (only_special_literals) {
-	iseq_add_mark_object(iseq, literals);
+	iseq_add_mark_object_compile_time(iseq, literals);
 
 	ADD_INSN(ret, nd_line(orig_node), dup);
 	ADD_INSN2(ret, nd_line(orig_node), opt_case_dispatch, literals, elselabel);
@@ -7285,6 +7288,7 @@ insn_data_to_s_detail(INSN *iobj)
 		    break;
 		}
 	      case TS_IC:	/* inline cache */
+	      case TS_ISE:	/* inline storage entry */
 		rb_str_catf(str, "<ic:%d>", FIX2INT(OPERAND_AT(iobj, j)));
 		break;
 	      case TS_CALLINFO: /* call info */
@@ -7524,7 +7528,6 @@ iseq_build_load_iseq(const rb_iseq_t *iseq, VALUE op)
     }
 
     loaded_iseq = rb_iseqw_to_iseq(iseqw);
-    iseq_add_mark_object(iseq, (VALUE)loaded_iseq);
     return loaded_iseq;
 }
 
@@ -7655,7 +7658,6 @@ iseq_build_from_ary_body(rb_iseq_t *iseq, LINK_ANCHOR *const anchor,
 			break;
 		      case TS_VALUE:
 			argv[j] = op;
-			iseq_add_mark_object(iseq, op);
 			break;
 		      case TS_ISEQ:
 			{
@@ -7672,6 +7674,7 @@ iseq_build_from_ary_body(rb_iseq_t *iseq, LINK_ANCHOR *const anchor,
 			argv[j] = (VALUE)rb_global_entry(SYM2ID(op));
 			break;
 		      case TS_IC:
+		      case TS_ISE:
 			argv[j] = op;
 			if (NUM2UINT(op) >= iseq->body->is_size) {
 			    iseq->body->is_size = NUM2INT(op) + 1;
@@ -7702,7 +7705,6 @@ iseq_build_from_ary_body(rb_iseq_t *iseq, LINK_ANCHOR *const anchor,
 			    }
 			    RB_GC_GUARD(op);
 			    argv[j] = map;
-			    rb_iseq_add_mark_object(iseq, map);
 			}
 			break;
 		      case TS_FUNCPTR:
@@ -8278,6 +8280,7 @@ ibf_dump_code(struct ibf_dump *dump, const rb_iseq_t *iseq)
 		code[code_index] = (VALUE)ibf_dump_iseq(dump, (const rb_iseq_t *)op);
 		break;
 	      case TS_IC:
+	      case TS_ISE:
 		{
 		    unsigned int i;
 		    for (i=0; i<iseq->body->is_size; i++) {
@@ -8343,6 +8346,7 @@ ibf_load_code(const struct ibf_load *load, const rb_iseq_t *iseq, const struct r
 		code[code_index] = (VALUE)ibf_load_iseq(load, (const rb_iseq_t *)op);
 		break;
 	      case TS_IC:
+	      case TS_ISE:
 		code[code_index] = (VALUE)&is_entries[(int)op];
 		break;
 	      case TS_CALLINFO:
@@ -8643,7 +8647,8 @@ ibf_dump_iseq_each(struct ibf_dump *dump, const rb_iseq_t *iseq)
     dump_body.is_entries =           NULL;
     dump_body.ci_entries =           ibf_dump_ci_entries(dump, iseq);
     dump_body.cc_entries =           NULL;
-    dump_body.mark_ary =             ISEQ_FLIP_CNT(iseq);
+    dump_body.variable.coverage      = Qnil;
+    dump_body.variable.original_iseq = Qnil;
 
     return ibf_dump_write(dump, &dump_body, sizeof(dump_body));
 }
@@ -8675,7 +8680,7 @@ ibf_load_iseq_each(const struct ibf_load *load, rb_iseq_t *iseq, ibf_offset_t of
     load_body->ci_kw_size = body->ci_kw_size;
     load_body->insns_info.size = body->insns_info.size;
 
-    RB_OBJ_WRITE(iseq, &load_body->mark_ary, iseq_mark_ary_create((int)body->mark_ary));
+    iseq_mark_ary_create(iseq, (int)body->variable.flip_count);
 
     {
 	VALUE realpath = Qnil, path = ibf_load_object(load, body->location.pathobj);
@@ -9306,7 +9311,6 @@ ibf_load_object(const struct ibf_load *load, VALUE object_index)
 
 	    rb_ary_store(load->obj_list, (long)object_index, obj);
 	}
-	iseq_add_mark_object(load->iseq, obj);
 	return obj;
     }
 }
@@ -9493,9 +9497,6 @@ ibf_load_iseq(const struct ibf_load *load, const rb_iseq_t *index_iseq)
 	    ibf_load_iseq_complete(iseq);
 #endif /* !USE_LAZY_LOAD */
 
-	    if (load->iseq) {
-		iseq_add_mark_object(load->iseq, (VALUE)iseq);
-	    }
 	    return iseq;
 	}
     }
diff --git a/insns.def b/insns.def
index eabace4ce1..77009d32f6 100644
--- a/insns.def
+++ b/insns.def
@@ -972,11 +972,11 @@ setinlinecache
 /* run iseq only once */
 DEFINE_INSN
 once
-(ISEQ iseq, IC ic)
+(ISEQ iseq, ISE ise)
 ()
 (VALUE val)
 {
-    val = vm_once_dispatch(ec, iseq, ic);
+    val = vm_once_dispatch(ec, iseq, ise);
 }
 
 /* case dispatcher, jump by table if possible */
diff --git a/iseq.c b/iseq.c
index 58e8eb8371..59a836139b 100644
--- a/iseq.c
+++ b/iseq.c
@@ -113,6 +113,100 @@ rb_iseq_free(const rb_iseq_t *iseq)
     RUBY_FREE_LEAVE("iseq");
 }
 
+#if OPT_DIRECT_THREADED_CODE || OPT_CALL_THREADED_CODE
+static int
+rb_vm_insn_addr2insn2(const void *addr)
+{
+    int insn;
+    const void * const *table = rb_vm_get_insns_address_table();
+
+    for (insn = 0; insn < VM_INSTRUCTION_SIZE; insn++) {
+	if (table[insn] == addr) {
+	    return insn;
+	}
+    }
+    rb_bug("rb_vm_insn_addr2insn: invalid insn address: %p", addr);
+}
+#endif
+
+static int
+rb_vm_insn_null_translator(const void *addr)
+{
+    return (int)addr;
+}
+
+typedef void iseq_value_itr_t(void *ctx, VALUE obj);
+typedef int rb_vm_insns_translator_t(const void *addr);
+
+static int
+iseq_extract_values(const VALUE *code, size_t pos, iseq_value_itr_t * func, void *data, rb_vm_insns_translator_t * translator)
+{
+    VALUE insn = translator((void *)code[pos]);
+    int len = insn_len(insn);
+    int op_no;
+    const char *types = insn_op_types(insn);
+
+    for (op_no = 0; types[op_no]; op_no++) {
+	char type = types[op_no];
+	switch (type) {
+	    case TS_CDHASH:
+	    case TS_ISEQ:
+	    case TS_VALUE:
+		{
+		    VALUE op = code[pos + op_no + 1];
+		    if (!SPECIAL_CONST_P(op)) {
+			func(data, op);
+		    }
+		    break;
+		}
+	    case TS_ISE:
+		{
+		    union iseq_inline_storage_entry *const is = (union iseq_inline_storage_entry *)code[pos + op_no + 1];
+		    if (is->once.value) {
+			func(data, is->once.value);
+		    }
+		    break;
+		}
+	    default:
+		break;
+	}
+    }
+
+    return len;
+}
+
+static void
+rb_iseq_each_value(const rb_iseq_t *iseq, iseq_value_itr_t * func, void *data)
+{
+    unsigned int size;
+    const VALUE *code;
+    size_t n;
+    rb_vm_insns_translator_t * translator;
+
+    size = iseq->body->iseq_size;
+    code = iseq->body->iseq_encoded;
+
+#if OPT_DIRECT_THREADED_CODE || OPT_CALL_THREADED_CODE
+    if (FL_TEST(iseq, ISEQ_TRANSLATED)) {
+	translator = rb_vm_insn_addr2insn2;
+    } else {
+	translator = rb_vm_insn_null_translator;
+    }
+#else
+    translator = rb_vm_insn_null_translator;
+#endif
+
+    for (n = 0; n < size;) {
+	n += iseq_extract_values(code, n, func, data, translator);
+    }
+}
+
+static void
+each_insn_value(void *ctx, VALUE obj)
+{
+    rb_gc_mark(obj);
+}
+
 void
 rb_iseq_mark(const rb_iseq_t *iseq)
 {
@@ -121,13 +215,31 @@ rb_iseq_mark(const rb_iseq_t *iseq)
     if (iseq->body) {
 	const struct rb_iseq_constant_body *body = iseq->body;
 
-	RUBY_MARK_UNLESS_NULL(body->mark_ary);
+	if(FL_TEST(iseq, ISEQ_MARKABLE_ISEQ)) {
+	    rb_iseq_each_value(iseq, each_insn_value, NULL);
+	}
+
+	rb_gc_mark(body->variable.coverage);
+	rb_gc_mark(body->variable.original_iseq);
 	rb_gc_mark(body->location.label);
 	rb_gc_mark(body->location.base_label);
 	rb_gc_mark(body->location.pathobj);
 	RUBY_MARK_UNLESS_NULL((VALUE)body->parent_iseq);
+
+	if (body->catch_table) {
+	    const struct iseq_catch_table *table = body->catch_table;
+	    unsigned int i;
+	    for(i = 0; i < table->size; i++) {
+		const struct iseq_catch_table_entry *entry;
+		entry = &table->entries[i];
+		if (entry->iseq) {
+		    rb_gc_mark((VALUE)entry->iseq);
+		}
+	    }
+	}
     }
 
+
     if (FL_TEST(iseq, ISEQ_NOT_LOADED_YET)) {
 	rb_gc_mark(iseq->aux.loader.obj);
     }
@@ -297,13 +409,6 @@ set_relation(rb_iseq_t *iseq, const rb_iseq_t *piseq)
     }
 }
 
-void
-rb_iseq_add_mark_object(const rb_iseq_t *iseq, VALUE obj)
-{
-    /* TODO: check dedup */
-    rb_ary_push(ISEQ_MARK_ARY(iseq), obj);
-}
-
 static VALUE
 prepare_iseq_build(rb_iseq_t *iseq,
 		   VALUE name, VALUE path, VALUE realpath, VALUE first_lineno, const rb_code_location_t *code_location,
@@ -324,7 +429,7 @@ prepare_iseq_build(rb_iseq_t *iseq,
     if (iseq != iseq->body->local_iseq) {
 	RB_OBJ_WRITE(iseq, &iseq->body->location.base_label, iseq->body->local_iseq->body->location.label);
     }
-    RB_OBJ_WRITE(iseq, &iseq->body->mark_ary, iseq_mark_ary_create(0));
+    iseq_mark_ary_create(iseq, 0);
 
     ISEQ_COMPILE_DATA_ALLOC(iseq);
     RB_OBJ_WRITE(iseq, &ISEQ_COMPILE_DATA(iseq)->err_info, err_info);
@@ -1610,6 +1715,7 @@ rb_insn_operand_intern(const rb_iseq_t *iseq,
 	break;
 
       case TS_IC:
+      case TS_ISE:
 	ret = rb_sprintf("<is:%"PRIdPTRDIFF">", (union iseq_inline_storage_entry *)op - iseq->body->is_entries);
 	break;
 
@@ -2353,6 +2459,7 @@ iseq_data_to_ary(const rb_iseq_t *iseq)
 		}
 		break;
 	      case TS_IC:
+	      case TS_ISE:
 		{
 		    union iseq_inline_storage_entry *is = (union iseq_inline_storage_entry *)*seq;
 		    rb_ary_push(ary, INT2FIX(is - iseq->body->is_entries));
diff --git a/iseq.h b/iseq.h
index 0c316e2cb2..31a3232e3b 100644
--- a/iseq.h
+++ b/iseq.h
@@ -28,44 +28,33 @@ rb_call_info_kw_arg_bytes(int keyword_len)
     return sizeof(struct rb_call_info_kw_arg) + sizeof(VALUE) * (keyword_len - 1);
 }
 
-enum iseq_mark_ary_index {
-    ISEQ_MARK_ARY_COVERAGE,
-    ISEQ_MARK_ARY_FLIP_CNT,
-    ISEQ_MARK_ARY_ORIGINAL_ISEQ,
-    ISEQ_MARK_ARY_INITIAL_SIZE
-};
-
-static inline VALUE
-iseq_mark_ary_create(int flip_cnt)
+static inline void
+iseq_mark_ary_create(rb_iseq_t *iseq, int flip_cnt)
 {
-    VALUE ary = rb_ary_tmp_new(ISEQ_MARK_ARY_INITIAL_SIZE);
-    rb_ary_push(ary, Qnil);              /* ISEQ_MARK_ARY_COVERAGE */
-    rb_ary_push(ary, INT2FIX(flip_cnt)); /* ISEQ_MARK_ARY_FLIP_CNT */
-    rb_ary_push(ary, Qnil);              /* ISEQ_MARK_ARY_ORIGINAL_ISEQ */
-    return ary;
+    RB_OBJ_WRITE(iseq, &iseq->body->variable.coverage, Qnil);
+    RB_OBJ_WRITE(iseq, &iseq->body->variable.original_iseq, Qnil);
+    iseq->body->variable.flip_count = flip_cnt;
 }
 
-#define ISEQ_MARK_ARY(iseq)           (iseq)->body->mark_ary
-
-#define ISEQ_COVERAGE(iseq)           RARRAY_AREF(ISEQ_MARK_ARY(iseq), ISEQ_MARK_ARY_COVERAGE)
-#define ISEQ_COVERAGE_SET(iseq, cov)  RARRAY_ASET(ISEQ_MARK_ARY(iseq), ISEQ_MARK_ARY_COVERAGE, cov)
+#define ISEQ_COVERAGE(iseq)           iseq->body->variable.coverage
+#define ISEQ_COVERAGE_SET(iseq, cov)  RB_OBJ_WRITE(iseq, &iseq->body->variable.coverage, cov)
 #define ISEQ_LINE_COVERAGE(iseq)      RARRAY_AREF(ISEQ_COVERAGE(iseq), COVERAGE_INDEX_LINES)
 #define ISEQ_BRANCH_COVERAGE(iseq)    RARRAY_AREF(ISEQ_COVERAGE(iseq), COVERAGE_INDEX_BRANCHES)
 
-#define ISEQ_FLIP_CNT(iseq) FIX2INT(RARRAY_AREF(ISEQ_MARK_ARY(iseq), ISEQ_MARK_ARY_FLIP_CNT))
+#define ISEQ_FLIP_CNT(iseq) (iseq)->body->variable.flip_count
 
 static inline int
 ISEQ_FLIP_CNT_INCREMENT(const rb_iseq_t *iseq)
 {
-    int cnt = ISEQ_FLIP_CNT(iseq);
-    RARRAY_ASET(ISEQ_MARK_ARY(iseq), ISEQ_MARK_ARY_FLIP_CNT, INT2FIX(cnt+1));
+    int cnt = iseq->body->variable.flip_count;
+    iseq->body->variable.flip_count += 1;
     return cnt;
 }
 
 static inline VALUE *
 ISEQ_ORIGINAL_ISEQ(const rb_iseq_t *iseq)
 {
-    VALUE str = RARRAY_AREF(ISEQ_MARK_ARY(iseq), ISEQ_MARK_ARY_ORIGINAL_ISEQ);
+    VALUE str = iseq->body->variable.original_iseq;
     if (RTEST(str)) return (VALUE *)RSTRING_PTR(str);
     return NULL;
 }
@@ -73,14 +62,14 @@ ISEQ_ORIGINAL_ISEQ(const rb_iseq_t *iseq)
 static inline void
 ISEQ_ORIGINAL_ISEQ_CLEAR(const rb_iseq_t *iseq)
 {
-    RARRAY_ASET(ISEQ_MARK_ARY(iseq), ISEQ_MARK_ARY_ORIGINAL_ISEQ, Qnil);
+    RB_OBJ_WRITE(iseq, &iseq->body->variable.original_iseq, Qnil);
 }
 
 static inline VALUE *
 ISEQ_ORIGINAL_ISEQ_ALLOC(const rb_iseq_t *iseq, long size)
 {
     VALUE str = rb_str_tmp_new(size * sizeof(VALUE));
-    RARRAY_ASET(ISEQ_MARK_ARY(iseq), ISEQ_MARK_ARY_ORIGINAL_ISEQ, str);
+    RB_OBJ_WRITE(iseq, &iseq->body->variable.original_iseq, str);
     return (VALUE *)RSTRING_PTR(str);
 }
 
@@ -94,6 +83,8 @@ ISEQ_ORIGINAL_ISEQ_ALLOC(const rb_iseq_t *iseq, long size)
 
 #define ISEQ_NOT_LOADED_YET   IMEMO_FL_USER1
 #define ISEQ_USE_COMPILE_DATA IMEMO_FL_USER2
+#define ISEQ_TRANSLATED       IMEMO_FL_USER3
+#define ISEQ_MARKABLE_ISEQ    IMEMO_FL_USER4
 
 struct iseq_compile_data {
     /* GC is needed */
@@ -173,7 +164,6 @@ void rb_iseq_build_from_ary(rb_iseq_t *iseq, VALUE misc,
 			    VALUE exception, VALUE body);
 
 /* iseq.c */
-void rb_iseq_add_mark_object(const rb_iseq_t *iseq, VALUE obj);
 VALUE rb_iseq_load(VALUE data, VALUE parent, VALUE opt);
 VALUE rb_iseq_parameters(const rb_iseq_t *iseq, int is_proc);
 struct st_table *ruby_insn_make_insn_table(void);
diff --git a/tool/ruby_vm/models/typemap.rb b/tool/ruby_vm/models/typemap.rb
index d818ce9878..7c5c872d7c 100644
--- a/tool/ruby_vm/models/typemap.rb
+++ b/tool/ruby_vm/models/typemap.rb
@@ -18,6 +18,7 @@
   "GENTRY"         => %w[G TS_GENTRY],
   "IC"             => %w[K TS_IC],
   "ID"             => %w[I TS_ID],
+  "ISE"            => %w[T TS_ISE],
   "ISEQ"           => %w[S TS_ISEQ],
   "OFFSET"         => %w[O TS_OFFSET],
   "VALUE"          => %w[V TS_VALUE],
diff --git a/vm_core.h b/vm_core.h
index 8bce7892b5..26187ff40e 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -407,7 +407,11 @@ struct rb_iseq_constant_body {
 				      */
     struct rb_call_cache *cc_entries; /* size is ci_size = ci_kw_size */
 
-    VALUE mark_ary;     /* Array: includes operands which should be GC marked */
+    struct {
+      rb_num_t flip_count;
+      VALUE coverage;
+      VALUE original_iseq;
+    } variable;
 
     unsigned int local_table_size;
     unsigned int is_size;
@@ -998,6 +1002,7 @@ enum vm_svar_index {
 
 /* inline cache */
 typedef struct iseq_inline_cache_entry *IC;
+typedef union iseq_inline_storage_entry *ISE;
 typedef struct rb_call_info *CALL_INFO;
 typedef struct rb_call_cache *CALL_CACHE;
 
diff --git a/vm_insnhelper.c b/vm_insnhelper.c
index acb7d7999d..8686877c76 100644
--- a/vm_insnhelper.c
+++ b/vm_insnhelper.c
@@ -3281,11 +3281,10 @@ vm_ic_update(IC ic, VALUE val, const VALUE *reg_ep)
 }
 
 static VALUE
-vm_once_dispatch(rb_execution_context_t *ec, ISEQ iseq, IC ic)
+vm_once_dispatch(rb_execution_context_t *ec, ISEQ iseq, ISE is)
 {
     rb_thread_t *th = rb_ec_thread_ptr(ec);
     rb_thread_t *const RUNNING_THREAD_ONCE_DONE = (rb_thread_t *)(0x1);
-    union iseq_inline_storage_entry *const is = (union iseq_inline_storage_entry *)ic;
 
   again:
     if (is->once.running_thread == RUNNING_THREAD_ONCE_DONE) {
@@ -3294,10 +3293,10 @@ vm_once_dispatch(rb_execution_context_t *ec, ISEQ iseq, IC ic)
     else if (is->once.running_thread == NULL) {
 	VALUE val;
 	is->once.running_thread = th;
-	val = is->once.value = rb_ensure(vm_once_exec, (VALUE)iseq, vm_once_clear, (VALUE)is);
+	val = rb_ensure(vm_once_exec, (VALUE)iseq, vm_once_clear, (VALUE)is);
+	RB_OBJ_WRITE(ec->cfp->iseq, &is->once.value, val);
 	/* is->once.running_thread is cleared by vm_once_clear() */
 	is->once.running_thread = RUNNING_THREAD_ONCE_DONE; /* success */
-	rb_iseq_add_mark_object(ec->cfp->iseq, val);
 	return val;
     }
     else if (is->once.running_thread == th) {