diff --git a/compile.c b/compile.c
index 61306209bf5cf3..c0cc0be873ef05 100644
--- a/compile.c
+++ b/compile.c
@@ -8625,7 +8625,8 @@ 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));
 }
@@ -8657,7 +8658,7 @@ 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);
diff --git a/iseq.c b/iseq.c
index 49f2765551db12..e59a612de8d635 100644
--- a/iseq.c
+++ b/iseq.c
@@ -216,7 +216,8 @@ rb_iseq_mark(const rb_iseq_t *iseq)
 	const struct rb_iseq_constant_body *body = iseq->body;
 
 	rb_iseq_each_value(iseq, each_insn_value, NULL);
-	RUBY_MARK_UNLESS_NULL(body->mark_ary);
+	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);
@@ -425,7 +426,7 @@ 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);
diff --git a/iseq.h b/iseq.h
index 0dd0703d207054..d238a55fe4d5f8 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);
 }
 
diff --git a/vm_core.h b/vm_core.h
index 8bce7892b52fce..e7e96e0ddf0d46 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;