diff --git a/lib/6to5/file.js b/lib/6to5/file.js
index 68cf3ce5e5..926cf0e427 100644
--- a/lib/6to5/file.js
+++ b/lib/6to5/file.js
@@ -78,6 +78,10 @@ File.normaliseOptions = function (opts) {
   opts.optional  = util.arrayify(opts.optional);
   opts.loose     = util.arrayify(opts.loose);
 
+  if (_.contains(opts.loose, "all")) {
+    opts.loose = Object.keys(transform.transformers);
+  }
+
   // todo: remove in 3.0.0
   _.each({
     fastForOf: "forOf",