diff --git a/depend b/depend
index 697a9a5eb7..8db2d7a675 100644
--- a/depend
+++ b/depend
@@ -16680,7 +16680,6 @@ shape.$(OBJEXT): $(top_srcdir)/internal/object.h
 shape.$(OBJEXT): $(top_srcdir)/internal/sanitizers.h
 shape.$(OBJEXT): $(top_srcdir)/internal/serial.h
 shape.$(OBJEXT): $(top_srcdir)/internal/set_table.h
-shape.$(OBJEXT): $(top_srcdir)/internal/st.h
 shape.$(OBJEXT): $(top_srcdir)/internal/static_assert.h
 shape.$(OBJEXT): $(top_srcdir)/internal/string.h
 shape.$(OBJEXT): $(top_srcdir)/internal/struct.h
diff --git a/internal/variable.h b/internal/variable.h
index d743a7033f..1b3c01f546 100644
--- a/internal/variable.h
+++ b/internal/variable.h
@@ -49,7 +49,7 @@ VALUE rb_mod_set_temporary_name(VALUE, VALUE);
 
 void rb_obj_replace_fields(VALUE obj, VALUE fields_obj);
 void rb_obj_copy_ivs_to_hash_table(VALUE obj, st_table *table);
-void rb_evict_ivars_to_hash(VALUE obj);
+VALUE rb_obj_complex_fields_build(VALUE obj);
 VALUE rb_obj_field_get(VALUE obj, shape_id_t target_shape_id);
 void rb_ivar_set_internal(VALUE obj, ID id, VALUE val);
 void rb_ivar_foreach_buffered(VALUE obj, int (*func)(ID name, VALUE val, st_data_t arg), st_data_t arg);
diff --git a/object.c b/object.c
index 52b80e1e2d..033b3dc35f 100644
--- a/object.c
+++ b/object.c
@@ -342,10 +342,7 @@ rb_obj_copy_ivar(VALUE dest, VALUE obj)
 
     shape_id_t dest_shape_id = rb_shape_rebuild(initial_shape_id, src_shape_id);
     if (UNLIKELY(rb_shape_complex_p(dest_shape_id))) {
-        VALUE fields_obj = rb_imemo_fields_new_complex(dest, dest_shape_id, rb_ivar_count(obj), false);
-        st_table *table = rb_imemo_fields_complex_tbl(fields_obj);
-        rb_obj_copy_ivs_to_hash_table(obj, table);
-        rb_obj_replace_fields(dest, fields_obj);
+        rb_obj_replace_fields(dest, rb_obj_complex_fields_build(obj));
         return;
     }
 
diff --git a/shape.c b/shape.c
index a0b12b4759..0004d4cc56 100644
--- a/shape.c
+++ b/shape.c
@@ -9,7 +9,6 @@
 #include "internal/object.h"
 #include "internal/symbol.h"
 #include "internal/variable.h"
-#include "internal/st.h"
 #include "variable.h"
 #include <stdbool.h>
 
@@ -1155,24 +1154,6 @@ rb_shape_copy_fields(VALUE dest, VALUE *dest_buf, shape_id_t dest_shape_id, VALU
     }
 }
 
-void
-rb_shape_copy_complex_ivars(VALUE dest, VALUE src)
-{
-    RUBY_ASSERT(IMEMO_TYPE_P(src, imemo_fields));
-    RUBY_ASSERT(IMEMO_TYPE_P(dest, imemo_fields));
-
-    shape_id_t dest_shape_id = RBASIC_SHAPE_ID(src);
-    st_table *dest_table = rb_imemo_fields_complex_tbl(dest);
-    st_replace(dest_table, rb_imemo_fields_complex_tbl(src));
-
-    if (rb_shape_has_object_id(dest_shape_id)) {
-        st_data_t stkey = (st_data_t)id_object_id;
-        st_delete(dest_table, &stkey, NULL);
-    }
-
-    RBASIC_SET_SHAPE_ID(dest, ROOT_COMPLEX_SHAPE_ID);
-}
-
 size_t
 rb_shape_edges_count(shape_id_t shape_id)
 {
diff --git a/shape.h b/shape.h
index 2c67d33123..c2cf158c72 100644
--- a/shape.h
+++ b/shape.h
@@ -267,7 +267,6 @@ shape_id_t rb_shape_transition_add_ivar_no_warnings(shape_id_t shape_id, ID id,
 shape_id_t rb_shape_object_id(shape_id_t original_shape_id);
 shape_id_t rb_shape_rebuild(shape_id_t initial_shape_id, shape_id_t dest_shape_id);
 void rb_shape_copy_fields(VALUE dest, VALUE *dest_buf, shape_id_t dest_shape_id, VALUE *src_buf, shape_id_t src_shape_id);
-void rb_shape_copy_complex_ivars(VALUE dest, VALUE src);
 
 static inline bool
 rb_shape_frozen_p(shape_id_t shape_id)
diff --git a/variable.c b/variable.c
index 27fab5c591..f78c35cac1 100644
--- a/variable.c
+++ b/variable.c
@@ -1623,20 +1623,13 @@ rb_evict_fields_to_hash(VALUE obj)
     return new_shape_id;
 }
 
-void
-rb_evict_ivars_to_hash(VALUE obj)
+VALUE
+rb_obj_complex_fields_build(VALUE obj)
 {
-    RUBY_ASSERT(RB_TYPE_P(obj, T_OBJECT));
-    RUBY_ASSERT(!rb_obj_shape_complex_p(obj));
-
-    shape_id_t new_shape_id = rb_obj_shape_transition_complex(obj);
-    VALUE fields_obj = rb_imemo_fields_new_complex(obj, new_shape_id, rb_ivar_count(obj), false);
+    VALUE fields_obj = rb_imemo_fields_new_complex(obj, ROOT_COMPLEX_SHAPE_ID, rb_ivar_count(obj), false);
     st_table *table = rb_imemo_fields_complex_tbl(fields_obj);
     rb_obj_copy_ivs_to_hash_table(obj, table);
-    ROBJECT_SET_EXTENDED(obj, fields_obj);
-    RBASIC_SET_FULL_SHAPE_ID(obj, rb_shape_transition_extended(new_shape_id));
-
-    RUBY_ASSERT(rb_obj_shape_complex_p(obj));
+    return fields_obj;
 }
 
 static VALUE
@@ -2290,10 +2283,7 @@ rb_copy_generic_ivar(VALUE dest, VALUE obj)
         shape_id_t dest_shape_id = rb_shape_rebuild(initial_shape_id, src_shape_id);
 
         if (UNLIKELY(rb_shape_complex_p(dest_shape_id))) {
-            new_fields_obj = rb_imemo_fields_new_complex(dest, dest_shape_id, rb_ivar_count(obj), false);
-            st_table *table = rb_imemo_fields_complex_tbl(new_fields_obj);
-            rb_obj_copy_ivs_to_hash_table(obj, table);
-            rb_obj_replace_fields(dest, new_fields_obj);
+            rb_obj_replace_fields(dest, rb_obj_complex_fields_build(obj));
             return;
         }