diff --git a/benchmark/ivar_extend.yml b/benchmark/ivar_extend.yml
new file mode 100644
index 0000000000..eb9ee923f5
--- /dev/null
+++ b/benchmark/ivar_extend.yml
@@ -0,0 +1,23 @@
+prelude: |
+  class Embedded
+    def initialize
+      @a = 1
+      @b = 1
+      @c = 1
+    end
+  end
+
+  class Extended
+    def initialize
+      @a = 1
+      @b = 1
+      @c = 1
+      @d = 1
+      @e = 1
+      @f = 1
+    end
+  end
+benchmark:
+  embedded: Embedded.new
+  extended: Extended.new
+loop_count: 20_000_000
diff --git a/gc.c b/gc.c
index 4d78b85543..1507be6642 100644
--- a/gc.c
+++ b/gc.c
@@ -2390,7 +2390,14 @@ VALUE
 rb_newobj_of(VALUE klass, VALUE flags)
 {
     if ((flags & RUBY_T_MASK) == T_OBJECT) {
-        return newobj_of(klass, (flags | ROBJECT_EMBED) & ~FL_WB_PROTECTED , Qundef, Qundef, Qundef, flags & FL_WB_PROTECTED);
+        st_table *index_tbl = RCLASS_IV_INDEX_TBL(klass);
+
+        VALUE obj = newobj_of(klass, (flags | ROBJECT_EMBED) & ~FL_WB_PROTECTED , Qundef, Qundef, Qundef, flags & FL_WB_PROTECTED);
+
+        if (index_tbl && index_tbl->num_entries > ROBJECT_EMBED_LEN_MAX) {
+            rb_init_iv_list(obj);
+        }
+        return obj;
     }
     else {
         return newobj_of(klass, flags & ~FL_WB_PROTECTED, 0, 0, 0, flags & FL_WB_PROTECTED);
@@ -2501,8 +2508,17 @@ rb_imemo_new_debug(enum imemo_type type, VALUE v1, VALUE v2, VALUE v3, VALUE v0,
 VALUE
 rb_class_allocate_instance(VALUE klass)
 {
+    st_table *index_tbl = RCLASS_IV_INDEX_TBL(klass);
+
     VALUE flags = T_OBJECT | ROBJECT_EMBED;
-    return newobj_of(klass, flags, Qundef, Qundef, Qundef, RGENGC_WB_PROTECTED_OBJECT);
+
+    VALUE obj = newobj_of(klass, flags, Qundef, Qundef, Qundef, RGENGC_WB_PROTECTED_OBJECT);
+
+    if (index_tbl && index_tbl->num_entries > ROBJECT_EMBED_LEN_MAX) {
+        rb_init_iv_list(obj);
+    }
+
+    return obj;
 }
 
 VALUE
diff --git a/object.c b/object.c
index c1e75d3854..d1e8ad78f0 100644
--- a/object.c
+++ b/object.c
@@ -324,24 +324,33 @@ rb_obj_singleton_class(VALUE obj)
 MJIT_FUNC_EXPORTED void
 rb_obj_copy_ivar(VALUE dest, VALUE obj)
 {
-    RUBY_ASSERT(RBASIC(dest)->flags & ROBJECT_EMBED);
+    VALUE *dst_buf = 0;
+    VALUE *src_buf = 0;
+    uint32_t len = ROBJECT_EMBED_LEN_MAX;
 
     if (RBASIC(obj)->flags & ROBJECT_EMBED) {
-	MEMCPY(ROBJECT(dest)->as.ary, ROBJECT(obj)->as.ary, VALUE, ROBJECT_EMBED_LEN_MAX);
-	RBASIC(dest)->flags |= ROBJECT_EMBED;
+        src_buf = ROBJECT(obj)->as.ary;
+
+        // embedded -> embedded
+        if (RBASIC(dest)->flags & ROBJECT_EMBED) {
+            dst_buf = ROBJECT(dest)->as.ary;
+        }
+        // embedded -> extended
+        else {
+            dst_buf = ROBJECT(dest)->as.heap.ivptr;
+        }
     }
+    // extended -> extended
     else {
-	uint32_t len = ROBJECT(obj)->as.heap.numiv;
-	VALUE *ptr = 0;
-	if (len > 0) {
-	    ptr = ALLOC_N(VALUE, len);
-	    MEMCPY(ptr, ROBJECT(obj)->as.heap.ivptr, VALUE, len);
-	}
-	ROBJECT(dest)->as.heap.ivptr = ptr;
-	ROBJECT(dest)->as.heap.numiv = len;
-	ROBJECT(dest)->as.heap.iv_index_tbl = ROBJECT(obj)->as.heap.iv_index_tbl;
-	RBASIC(dest)->flags &= ~ROBJECT_EMBED;
+        uint32_t src_len = ROBJECT(obj)->as.heap.numiv;
+        uint32_t dst_len = ROBJECT(dest)->as.heap.numiv;
+
+        len = src_len < dst_len ? src_len : dst_len;
+        dst_buf = ROBJECT(dest)->as.heap.ivptr;
+        src_buf = ROBJECT(obj)->as.heap.ivptr;
     }
+
+    MEMCPY(dst_buf, src_buf, VALUE, len);
 }
 
 static void