diff --git a/activemodel/lib/active_model/attribute.rb b/activemodel/lib/active_model/attribute.rb
index 43130c37c5..b75ff80b31 100644
--- a/activemodel/lib/active_model/attribute.rb
+++ b/activemodel/lib/active_model/attribute.rb
@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require "active_support/core_ext/object/duplicable"
+
 module ActiveModel
   class Attribute # :nodoc:
     class << self
diff --git a/activemodel/test/cases/attribute_set_test.rb b/activemodel/test/cases/attribute_set_test.rb
index d50e6cfa7a..50484cb9ce 100644
--- a/activemodel/test/cases/attribute_set_test.rb
+++ b/activemodel/test/cases/attribute_set_test.rb
@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
 require "cases/helper"
+require "active_model/attribute_set"
+require "active_model/type"
 
 module ActiveModel
   class AttributeSetTest < ActiveModel::TestCase