diff --git a/activemodel/lib/active_model/dirty.rb b/activemodel/lib/active_model/dirty.rb
index 0ab8df42f5..80e2814b00 100644
--- a/activemodel/lib/active_model/dirty.rb
+++ b/activemodel/lib/active_model/dirty.rb
@@ -26,6 +26,10 @@ module ActiveModel
   #
   #     define_attribute_methods :name
   #
+  #     def initialize(name)
+  #       @name = name
+  #     end
+  #
   #     def name
   #       @name
   #     end
@@ -54,7 +58,7 @@ module ActiveModel
   #
   # A newly instantiated +Person+ object is unchanged:
   #
-  #   person = Person.new
+  #   person = Person.new(name: "Uncle Bob")
   #   person.changed? # => false
   #
   # Change the name: