add_filter( 'upload_mimes', 'iworks_custom_upload_mimes' ); function iworks_custom_upload_mimes ( $existing_mimes=array() ) { $existing_mimes['gzip'] = 'application/x-gzip'; $existing_mimes['gz'] = 'application/x-gzip'; $existing_mimes['zip'] = 'application/zip'; $existing_mimes['csv'] = 'text/csv'; return $existing_mimes; }