diff --git a/activerecord/lib/active_record/named_scope.rb b/activerecord/lib/active_record/named_scope.rb
index 83043c2..1dd37af 100644
--- a/activerecord/lib/active_record/named_scope.rb
+++ b/activerecord/lib/active_record/named_scope.rb
@@ -88,7 +88,12 @@ module ActiveRecord
             when Hash
               options
             when Proc
-              options.call(*args)
+              # Make sure named_scope is invoking lambda from right self context
+              if self.model_name != parent_scope.model_name
+                parent_scope.instance_exec(*args, &options)
+              else
+                options.call(*args)
+              end
           end, &block)
         end
         (class << self; self end).instance_eval do
diff --git a/activerecord/test/cases/named_scope_test.rb b/activerecord/test/cases/named_scope_test.rb
index 64e8997..850a450 100644
--- a/activerecord/test/cases/named_scope_test.rb
+++ b/activerecord/test/cases/named_scope_test.rb
@@ -5,6 +5,7 @@ require 'models/comment'
 require 'models/reply'
 require 'models/author'
 require 'models/developer'
+require 'models/company'
 
 class NamedScopeTest < ActiveRecord::TestCase
   fixtures :posts, :authors, :topics, :comments, :author_addresses
@@ -277,4 +278,10 @@ class NamedScopeTest < ActiveRecord::TestCase
     post = Post.find(1)
     assert_equal post.comments.size, Post.scoped(:joins => join).scoped(:joins => join, :conditions => "posts.id = #{post.id}").size
   end
+
+  def test_sti_named_scope
+    firm_includes = Firm.scopes[:include_all].call(Firm, :all).proxy_options[:include]
+    firm_reflections_keys = Firm.reflections.keys
+    assert_equal firm_includes, firm_reflections_keys
+  end
 end
diff --git a/activerecord/test/models/company.rb b/activerecord/test/models/company.rb
index 0e3fafa..e5be682 100644
--- a/activerecord/test/models/company.rb
+++ b/activerecord/test/models/company.rb
@@ -1,5 +1,6 @@
 class AbstractCompany < ActiveRecord::Base
   self.abstract_class = true
+  named_scope :include_all, lambda { { :include => self.reflections.keys } }
 end
 
 class Company < AbstractCompany