If special ActiveModel methods like #id, #errors, and #to_param are defined directly on the decorator, do not redefine them as proxy methods.

lib/draper/active_model_support.rb

@@ -13,8 +13,10 @@ module Draper::ActiveModelSupport
           class << base
             self
           end.class_eval do
-            send(:define_method, method_name) do |*args, &block|
-              model.send(method_name, *args, &block)
+            if !base.class.instance_methods.include?(method_name) || base.class.instance_method(method_name).owner === Draper::Base
+              send(:define_method, method_name) do |*args, &block|
+                model.send(method_name, *args, &block)
+              end
             end
           end
         end

spec/draper/base_spec.rb

@@ -215,19 +215,33 @@ describe Draper::Base do
     end
 
     context "when an ActiveModel descendant" do
-      it "should always proxy to_param" do
+      it "should always proxy to_param if it is not defined on the decorator itself" do
         source.stub(:to_param).and_return(1)
         Draper::Base.new(source).to_param.should == 1
       end
 
-      it "should always proxy id" do
+      it "should always proxy id if it is not defined on the decorator itself" do
         source.stub(:id).and_return(123456789)
         Draper::Base.new(source).id.should == 123456789
       end
 
-      it "should always proxy errors" do
+      it "should always proxy errors if it is not defined on the decorator itself" do
         Draper::Base.new(source).errors.should be_an_instance_of ActiveModel::Errors
       end
+
+      it "should never proxy to_param if it is defined on the decorator itself" do
+        source.stub(:to_param).and_return(1)
+        DecoratorWithSpecialMethods.new(source).to_param.should == "foo"
+      end
+
+      it "should never proxy id if it is defined on the decorator itself" do
+        source.stub(:id).and_return(123456789)
+        DecoratorWithSpecialMethods.new(source).id.should == 1337
+      end
+
+      it "should never proxy errors if it is defined on the decorator itself" do
+        DecoratorWithSpecialMethods.new(source).errors.should be_an_instance_of Array
+      end
     end
 
     context "when not an ActiveModel descendant" do

spec/spec_helper.rb

@@ -14,6 +14,7 @@ require './spec/support/samples/decorator_with_allows'
 require './spec/support/samples/decorator_with_multiple_allows'
 require './spec/support/samples/decorator_with_application_helper'
 require './spec/support/samples/decorator_with_denies'
+require './spec/support/samples/decorator_with_special_methods'
 require './spec/support/samples/namespaced_product'
 require './spec/support/samples/namespaced_product_decorator'
 require './spec/support/samples/non_active_model_product'