diff --git a/activesupport/lib/active_support/core_ext/object/duplicable.rb b/activesupport/lib/active_support/core_ext/object/duplicable.rb
index 9d1630bb7c..dd63b64c77 100644
--- a/activesupport/lib/active_support/core_ext/object/duplicable.rb
+++ b/activesupport/lib/active_support/core_ext/object/duplicable.rb
@@ -81,30 +81,6 @@ class Numeric
   end
 end
 
-class Class
-  # Classes are not duplicable:
-  #
-  #  c = Class.new # => #<Class:0x10328fd80>
-  #  c.dup         # => #<Class:0x10328fd80>
-  #
-  # Note +dup+ returned the same class object.
-  def duplicable?
-    false
-  end
-end
-
-class Module
-  # Modules are not duplicable:
-  #
-  #  m = Module.new # => #<Module:0x10328b6e0>
-  #  m.dup          # => #<Module:0x10328b6e0>
-  #
-  # Note +dup+ returned the same module object.
-  def duplicable?
-    false
-  end
-end
-
 require 'bigdecimal'
 class BigDecimal
   begin
diff --git a/activesupport/test/core_ext/duplicable_test.rb b/activesupport/test/core_ext/duplicable_test.rb
index 1105353e45..e0566e012c 100644
--- a/activesupport/test/core_ext/duplicable_test.rb
+++ b/activesupport/test/core_ext/duplicable_test.rb
@@ -5,8 +5,8 @@ require 'active_support/core_ext/numeric/time'
 
 class DuplicableTest < ActiveSupport::TestCase
   RAISE_DUP  = [nil, false, true, :symbol, 1, 2.3, 5.seconds]
-  YES = ['1', Object.new, /foo/, [], {}, Time.now]
-  NO = [Class.new, Module.new]
+  YES = ['1', Object.new, /foo/, [], {}, Time.now, Class.new, Module.new]
+  NO = []
 
   begin
     bd = BigDecimal.new('4.56')