diff --git a/activemodel/lib/active_model/attribute.rb b/activemodel/lib/active_model/attribute.rb
index 3561c5207e..193f44932f 100644
--- a/activemodel/lib/active_model/attribute.rb
+++ b/activemodel/lib/active_model/attribute.rb
@@ -175,19 +175,6 @@ module ActiveModel
           type.deserialize(value)
         end
 
-        def forgetting_assignment
-          # If this attribute was not persisted (with a `value_for_database`
-          # that might differ from `value_before_type_cast`) and `value` has not
-          # changed in place, we can simply dup this attribute to avoid
-          # deserialize / cast / serialize calls from computing the new
-          # attribute's `value_before_type_cast`.
-          if !defined?(@value_for_database) && !changed_in_place?
-            dup
-          else
-            super
-          end
-        end
-
         private
           def _original_value_for_database
             value_before_type_cast