diff --git a/app/serializers/learning_object_serializer.rb b/app/serializers/learning_object_serializer.rb
index ddfb352bfef79ee1dca9bcbc815434be1e1d52a1..4fd841146b703a7183ea3f717255bce9388e9300 100644
--- a/app/serializers/learning_object_serializer.rb
+++ b/app/serializers/learning_object_serializer.rb
@@ -4,10 +4,14 @@ class LearningObjectSerializer < ActiveModel::Serializer
   end
 
   def default_mime_type
-    object.default_attachment.try(:retrieve_url)
+    object.default_attachment.try(:mime_type)
+  end
+
+  def default_attachment_id
+    object.default_attachment.try(:id)
   end
 
-  attributes :id, :name, :description, :author, :thumbnail, :publisher, :language, :default_location, :default_mime_type, :score, :license, :likes_count, :shares_count, :created_at, :updated_at
+  attributes :id, :name, :description, :author, :thumbnail, :publisher, :language, :default_attachment_id, :default_location, :default_mime_type, :score, :license, :likes_count, :shares_count, :created_at, :updated_at
 
   has_many :tags
   has_many :attachments