diff --git a/lib/active_type/util/unmutable_attributes.rb b/lib/active_type/util/unmutable_attributes.rb
index 42b4d12..c923d93 100644
--- a/lib/active_type/util/unmutable_attributes.rb
+++ b/lib/active_type/util/unmutable_attributes.rb
@@ -10,6 +10,7 @@ module Util
     class UnmutableAttributes
 
       attr_reader :original_attributes
+      delegate :to_hash, to: :original_attributes
 
       def initialize(attributes)
         @original_attributes = attributes
diff --git a/spec/active_type/util_spec.rb b/spec/active_type/util_spec.rb
index 7b60c02..e902292 100644
--- a/spec/active_type/util_spec.rb
+++ b/spec/active_type/util_spec.rb
@@ -271,7 +271,7 @@ class AssociatedRecord < ActiveRecord::Base
           base_record = UtilSpec::BaseRecord.create!(persisted_string: 'foo')
           ActiveType::Util.cast(base_record, UtilSpec::ExtendedRecord)
 
-          expect(base_record.attributes).to eq({ 'persisted_string' => 'foo'})
+          expect(base_record.attributes).to include('persisted_string' => 'foo')
         end
 
         context 'with option force: true' do