diff --git a/lib/6to5/transformation/file.js b/lib/6to5/transformation/file.js
index 7fe68801e1..5b33ee1933 100644
--- a/lib/6to5/transformation/file.js
+++ b/lib/6to5/transformation/file.js
@@ -136,7 +136,7 @@ File.prototype.normalizeOptions = function (opts) {
   opts.optional  = util.arrayify(opts.optional);
   opts.loose     = util.arrayify(opts.loose);
 
-  if (includes(opts.loose, "all")) {
+  if (includes(opts.loose, "all") || includes(opts.loose, true)) {
     opts.loose = Object.keys(transform.transformers);
   }