Rails: radio button selection for nested forms objects

I have the following form for photo_album which uses the nested forms feature of the Rails in saving the photos while updating the photo_album. And having trouble with the selection of radio button value. I want only one of the photos be able to select as the album cover, but due to the way rails produces form element ids and names, I am able to select all of the photos as album covers. Is there any workaround?

<% form_for @photo_album do |f| %>   <%= f.error_messages %>

  <% @photo_album.photos.each do |photo| %>     <% f.fields_for :photos, photo do |photo_fields| %>       <p>        <%= image_tag url_for_image_column(photo, "data", :thumb) %>       </p>       <p>        <%= photo_fields.label :title %>        <%= photo_fields.text_field :title %>       </p>       <p>        <%= photo_fields.label :body %>        <%= photo_fields.text_area :body %>       </p>       <p>        <%= photo_fields.radio_button :cover, "1" %>        <%= photo_fields.label :cover, 'Album Cover', :class => 'option' %>        <%= photo_fields.check_box :_delete %>        <%= photo_fields.label :_delete, 'Delete', :class => 'option' %>       </p>      <% end %>    <% end %>

   <p>      <%= f.submit @photo_album.new_record? ? 'Create' : 'Update' %>     </p> <% end %>

And following is the html produced by rails (which is part of the problem) for radio buttons:

<p> <input type="radio" value="1" name="photo_album[photos_attributes][0][cover]" id="photo_album_photos_attributes_0_cover_1"/> <label for="photo_album_photos_attributes_0_cover" class="option">Album Cover</label> <input type="hidden" value="0" name="photo_album[photos_attributes][0][_delete]"/><input type="checkbox" value="1" name="photo_album[photos_attributes][0][_delete]" id="photo_album_photos_attributes_0__delete"/> <label for="photo_album_photos_attributes_0__delete" class="option">Delete</label> </p>