add class to this php code?

add_filter('the_content', 'alc_image_spanner');

  function alc_image_spanner($text) {
    $text = preg_replace_callback("#<img(.*?)>#is", create_function('$matches', 'return "<span><img".$matches[1]."></span>";'), $text);
    return $text;
  }

when i add a class like this

add_filter('the_content', 'alc_image_spanner');

  function alc_image_spanner($text) {
    $text = preg_replace_callback("#<img(.*?)>#is", create_function('$matches', 'return "<span class="gallery"><img".$matches[1]."></span>";'), $text);
    return $text;
  }

i get FATAL ERROR : SCREAM: Error suppression ignored for […]

any help would be great thanks