diff --git a/activerecord/lib/active_record/persistence.rb b/activerecord/lib/active_record/persistence.rb
index 309bb980e3..b94ef18fd5 100644
--- a/activerecord/lib/active_record/persistence.rb
+++ b/activerecord/lib/active_record/persistence.rb
@@ -181,7 +181,7 @@ module ActiveRecord
       became = klass.new
       became.instance_variable_set("@attributes", @attributes)
       became.instance_variable_set("@attributes_cache", @attributes_cache)
-      became.instance_variable_set("@changed_attributes", @changed_attributes)
+      became.instance_variable_set("@changed_attributes", @changed_attributes) if defined?(@changed_attributes)
       became.instance_variable_set("@new_record", new_record?)
       became.instance_variable_set("@destroyed", destroyed?)
       became.instance_variable_set("@errors", errors)