diff --git a/gc.c b/gc.c
index c720971b70..fe5c5cff0d 100644
--- a/gc.c
+++ b/gc.c
@@ -373,7 +373,7 @@ rb_gc_get_shape(VALUE obj)
 void
 rb_gc_set_shape(VALUE obj, uint32_t shape_id)
 {
-    rb_shape_set_shape_id(obj, (uint32_t)shape_id);
+    rb_obj_set_shape_id(obj, (uint32_t)shape_id);
 }
 
 uint32_t
diff --git a/object.c b/object.c
index 97fe0afa74..99950d477f 100644
--- a/object.c
+++ b/object.c
@@ -362,7 +362,7 @@ rb_obj_copy_ivar(VALUE dest, VALUE obj)
     }
 
     rb_shape_copy_fields(dest, dest_buf, dest_shape_id, obj, src_buf, src_shape_id);
-    rb_shape_set_shape_id(dest, dest_shape_id);
+    rb_obj_set_shape_id(dest, dest_shape_id);
 }
 
 static void
@@ -500,7 +500,7 @@ rb_obj_clone_setup(VALUE obj, VALUE clone, VALUE kwfreeze)
                 rb_evict_ivars_to_hash(clone);
             }
             else {
-                rb_shape_set_shape_id(clone, next_shape_id);
+                rb_obj_set_shape_id(clone, next_shape_id);
             }
         }
         break;
@@ -524,7 +524,7 @@ rb_obj_clone_setup(VALUE obj, VALUE clone, VALUE kwfreeze)
             rb_evict_ivars_to_hash(clone);
         }
         else {
-            rb_shape_set_shape_id(clone, next_shape_id);
+            rb_obj_set_shape_id(clone, next_shape_id);
         }
         break;
       }
diff --git a/shape.h b/shape.h
index ee522a48e5..91f1931290 100644
--- a/shape.h
+++ b/shape.h
@@ -230,7 +230,7 @@ RBASIC_FIELDS_COUNT(VALUE obj)
 
 shape_id_t rb_shape_traverse_from_new_root(shape_id_t initial_shape_id, shape_id_t orig_shape_id);
 
-bool rb_shape_set_shape_id(VALUE obj, shape_id_t shape_id);
+bool rb_obj_set_shape_id(VALUE obj, shape_id_t shape_id);
 
 static inline bool
 rb_shape_obj_has_id(VALUE obj)
diff --git a/string.c b/string.c
index a922c9269a..faa4a16106 100644
--- a/string.c
+++ b/string.c
@@ -959,8 +959,7 @@ static VALUE
 setup_fake_str(struct RString *fake_str, const char *name, long len, int encidx)
 {
     fake_str->basic.flags = T_STRING|RSTRING_NOEMBED|STR_NOFREE|STR_FAKESTR;
-
-    rb_shape_set_shape_id((VALUE)fake_str, 0);
+    RBASIC_SET_SHAPE_ID((VALUE)fake_str, ROOT_SHAPE_ID);
 
     if (!name) {
         RUBY_ASSERT_ALWAYS(len == 0);
diff --git a/variable.c b/variable.c
index 5c83ec955a..c29ca02390 100644
--- a/variable.c
+++ b/variable.c
@@ -1554,7 +1554,7 @@ rb_ivar_delete(VALUE obj, ID id, VALUE undef)
         MEMCPY(ROBJECT_FIELDS(obj), fields, VALUE, new_fields_count);
         xfree(fields);
     }
-    rb_shape_set_shape_id(obj, next_shape_id);
+    rb_obj_set_shape_id(obj, next_shape_id);
 
     if (locked) {
         RB_VM_LOCK_LEAVE_LEV(&lev);
@@ -1617,13 +1617,13 @@ obj_transition_too_complex(VALUE obj, st_table *table)
         if (!(RBASIC(obj)->flags & ROBJECT_EMBED)) {
             old_fields = ROBJECT_FIELDS(obj);
         }
-        rb_shape_set_shape_id(obj, shape_id);
+        rb_obj_set_shape_id(obj, shape_id);
         ROBJECT_SET_FIELDS_HASH(obj, table);
         break;
       case T_CLASS:
       case T_MODULE:
         old_fields = RCLASS_PRIME_FIELDS(obj);
-        rb_shape_set_shape_id(obj, shape_id);
+        rb_obj_set_shape_id(obj, shape_id);
         RCLASS_SET_FIELDS_HASH(obj, table);
         break;
       default:
@@ -1638,7 +1638,7 @@ obj_transition_too_complex(VALUE obj, st_table *table)
                  * and hold the table because the xmalloc could trigger a GC
                  * compaction. We want the table to be updated rather than
                  * the original fields. */
-                rb_shape_set_shape_id(obj, shape_id);
+                rb_obj_set_shape_id(obj, shape_id);
                 old_fields_tbl->as.complex.table = table;
                 old_fields = (VALUE *)old_fields_tbl;
             }
@@ -1647,7 +1647,7 @@ obj_transition_too_complex(VALUE obj, st_table *table)
             fields_tbl->as.complex.table = table;
             st_insert(gen_ivs, (st_data_t)obj, (st_data_t)fields_tbl);
 
-            rb_shape_set_shape_id(obj, shape_id);
+            rb_obj_set_shape_id(obj, shape_id);
         }
     }
 
@@ -1831,7 +1831,7 @@ generic_fields_lookup_ensure_size(st_data_t *k, st_data_t *v, st_data_t u, int e
 
     fields_lookup->fields_tbl = fields_tbl;
     if (fields_lookup->shape_id) {
-        rb_shape_set_shape_id(fields_lookup->obj, fields_lookup->shape_id);
+        rb_obj_set_shape_id(fields_lookup->obj, fields_lookup->shape_id);
     }
 
     return ST_CONTINUE;
@@ -1986,7 +1986,7 @@ obj_ivar_set_shape_resize_fields(VALUE obj, attr_index_t old_capa, attr_index_t
 static void
 obj_ivar_set_set_shape_id(VALUE obj, shape_id_t shape_id, void *_data)
 {
-    rb_shape_set_shape_id(obj, shape_id);
+    rb_obj_set_shape_id(obj, shape_id);
 }
 
 static void
@@ -2038,7 +2038,7 @@ rb_vm_set_ivar_id(VALUE obj, ID id, VALUE val)
 }
 
 bool
-rb_shape_set_shape_id(VALUE obj, shape_id_t shape_id)
+rb_obj_set_shape_id(VALUE obj, shape_id_t shape_id)
 {
     if (rb_obj_shape_id(obj) == shape_id) {
         return false;
@@ -2063,7 +2063,7 @@ void rb_obj_freeze_inline(VALUE x)
         if (rb_shape_too_complex_p(next_shape_id) && !rb_shape_obj_too_complex_p(x)) {
             rb_evict_fields_to_hash(x);
         }
-        rb_shape_set_shape_id(x, next_shape_id);
+        rb_obj_set_shape_id(x, next_shape_id);
 
         if (RBASIC_CLASS(x)) {
             rb_freeze_singleton_class(x);
@@ -2354,7 +2354,7 @@ rb_copy_generic_ivar(VALUE dest, VALUE obj)
         }
 
         if (!RSHAPE(dest_shape_id)->capacity) {
-            rb_shape_set_shape_id(dest, dest_shape_id);
+            rb_obj_set_shape_id(dest, dest_shape_id);
             FL_UNSET(dest, FL_EXIVAR);
             return;
         }
@@ -2375,7 +2375,7 @@ rb_copy_generic_ivar(VALUE dest, VALUE obj)
             st_insert(generic_fields_tbl_no_ractor_check(obj), (st_data_t)dest, (st_data_t)new_fields_tbl);
         }
 
-        rb_shape_set_shape_id(dest, dest_shape_id);
+        rb_obj_set_shape_id(dest, dest_shape_id);
     }
     return;
 
@@ -4671,7 +4671,7 @@ class_ivar_set_shape_resize_fields(VALUE obj, attr_index_t _old_capa, attr_index
 static void
 class_ivar_set_set_shape_id(VALUE obj, shape_id_t shape_id, void *_data)
 {
-    rb_shape_set_shape_id(obj, shape_id);
+    rb_obj_set_shape_id(obj, shape_id);
 }
 
 static void