diff --git a/platform/delete.backup.provision.inc b/platform/delete.backup.provision.inc
index 0e2e5fb..1b86e8a 100644
--- a/platform/delete.backup.provision.inc
+++ b/platform/delete.backup.provision.inc
@@ -9,32 +9,33 @@
  *
  * These are the hooks that will be executed by the drush_invoke function
  * when deleting a backup file from the backend.
+ *
+ * @param string $backup
+ *   A comma-separated list of backup filenames.
  */
-function drush_provision_drupal_provision_backup_delete($backup = NULL) {
-  if ($backup) {
-    $backups = explode(',', $backup);
-    foreach ($backups as $filename) {
-      $success = provision_file()->unlink($filename)
-         ->succeed('Removed backup file @path')
-         ->fail('Could not remove backup file @path');
-    }
-  }
-  else {
-    drush_set_error(dt('No backup files provided'));
+function drush_provision_drupal_provision_backup_delete($backup) {
+  $backups = explode(',', $backup);
+  foreach ($backups as $filename) {
+    $success = provision_file()->unlink($filename)
+      ->succeed('Removed backup file @path')
+      ->fail('Could not remove backup file @path');
   }
 }
 
 /**
  * Implements drush_hook_post_COMMAND().
  *
- * If we have a client name and backups provided, cleanup the backup
- * symlinks created for that client.
+ * If we have a client name, cleanup the backup symlinks created for that
+ * client.
  *
  * Will not provoke a rollback if there is no symlink, for backward
  * compatibility.
+ *
+ * @param string $backup
+ *   A comma-separated list of backup filenames.
  */
-function drush_provision_drupal_post_provision_backup_delete($backup = NULL) {
-  if ($backup && d()->client_name) {
+function drush_provision_drupal_post_provision_backup_delete($backup) {
+  if (d()->client_name) {
     $backup_dir = d()->server->clients_path . '/' . d()->client_name . '/backups';
     $backups = explode(',', $backup);
     foreach ($backups as $filename) {
diff --git a/provision.drush.inc b/provision.drush.inc
index fe0e22e..279e832 100644
--- a/provision.drush.inc
+++ b/provision.drush.inc
@@ -279,6 +279,7 @@ function provision_drush_command() {
   $items['provision-backup-delete'] = array(
     'description' => 'Delete a backup file.',
     'arguments' => array('backup-file' => dt('The backup file to delete. This will be a gzipped tarball.')),
+		'required-arguments' => TRUE,
     'examples' => array(
       'drush @site provision-backup-delete /path/to/site_backup.tgz' => 'Delete a backup of this site as defined by the site Drush alias generated with provision-save.',
     ),