diff --git a/activerecord/lib/active_record/associations/association_proxy.rb b/activerecord/lib/active_record/associations/association_proxy.rb
index 241b9bf..bfd511a 100644
--- a/activerecord/lib/active_record/associations/association_proxy.rb
+++ b/activerecord/lib/active_record/associations/association_proxy.rb
@@ -178,7 +178,7 @@ module ActiveRecord
         def set_belongs_to_association_for(record)
           if @reflection.options[:as]
             record["#{@reflection.options[:as]}_id"]   = @owner.id unless @owner.new_record?
-            record["#{@reflection.options[:as]}_type"] = @owner.class.base_class.name.to_s
+            record["#{@reflection.options[:as]}_type"] = @owner.class.name.to_s
           else
             unless @owner.new_record?
               primary_key = @reflection.options[:primary_key] || :id
diff --git a/activerecord/test/cases/associations/join_model_test.rb b/activerecord/test/cases/associations/join_model_test.rb
index 21412d1..feaedcb 100644
--- a/activerecord/test/cases/associations/join_model_test.rb
+++ b/activerecord/test/cases/associations/join_model_test.rb
@@ -144,13 +144,13 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
   def test_set_polymorphic_has_many
     tagging = tags(:misc).taggings.create
     posts(:thinking).taggings << tagging
-    assert_equal "Post", tagging.taggable_type
+    assert_equal "SpecialPost", tagging.taggable_type
   end
 
   def test_set_polymorphic_has_one
     tagging = tags(:misc).taggings.create
     posts(:thinking).tagging = tagging
-    assert_equal "Post", tagging.taggable_type
+    assert_equal "SpecialPost", tagging.taggable_type
   end
 
   def test_create_polymorphic_has_many_with_scope