diff --git a/activerecord/lib/active_record/associations/association_proxy.rb b/activerecord/lib/active_record/associations/association_proxy.rb
index 40a605c4fac7a3f02134dff8403fb7c06a009504..739dbbcb10679639cb2cc3081f1c349f1365da12 100644
--- a/activerecord/lib/active_record/associations/association_proxy.rb
+++ b/activerecord/lib/active_record/associations/association_proxy.rb
@@ -47,14 +47,29 @@ module Associations
     # instantiation of the actual post records.
     class AssociationProxy #:nodoc:
       alias_method :proxy_respond_to?, :respond_to?
-      alias_method :proxy_extend, :extend
       delegate :to_param, :to => :proxy_target
       instance_methods.each { |m| undef_method m unless m.to_s =~ /^(?:nil\?|send|object_id)$|^__|^respond_to_missing|proxy_/ }
 
+      def self.new(owner, reflection)
+        klass =
+          reflection.cached_extend_class ||=
+            if reflection.options[:extend]
+              const_name = "AR_CACHED_EXTEND_CLASS_#{reflection.name}_#{reflection.options[:extend].join("_").gsub("::","_")}"
+              reflection.active_record.const_set(const_name, Class.new(self) do
+                include *reflection.options[:extend]
+              end)
+            else
+              self
+            end
+
+        proxy = klass.allocate
+        proxy.send(:initialize, owner, reflection)
+        proxy
+      end
+
       def initialize(owner, reflection)
         @owner, @reflection = owner, reflection
         reflection.check_validity!
-        Array(reflection.options[:extend]).each { |ext| proxy_extend(ext) }
         reset
       end
 
diff --git a/activerecord/lib/active_record/reflection.rb b/activerecord/lib/active_record/reflection.rb
index 13bcb8b1afb67bae9f45ac36085665b49562ec48..b3a81f728381126edc2a8b0f0c4b86c8305efed6 100644
--- a/activerecord/lib/active_record/reflection.rb
+++ b/activerecord/lib/active_record/reflection.rb
@@ -77,6 +77,7 @@ def reflect_on_all_autosave_associations
     # those classes. Objects of AggregateReflection and AssociationReflection are returned by the Reflection::ClassMethods.
     class MacroReflection
       attr_reader :active_record
+      attr_accessor :cached_extend_class
 
       def initialize(macro, name, options, active_record)
         @macro, @name, @options, @active_record = macro, name, options, active_record