diff --git a/lib/6to5/transformation/transformer.js b/lib/6to5/transformation/transformer.js
index 7239e5e976..d9587a38c0 100644
--- a/lib/6to5/transformation/transformer.js
+++ b/lib/6to5/transformation/transformer.js
@@ -8,20 +8,25 @@ function Transformer(key, transformer, opts) {
   this.manipulateOptions = transformer.manipulateOptions;
   this.experimental      = !!transformer.experimental;
   this.secondPass        = !!transformer.secondPass;
-  this.transformer       = Transformer.normalise(transformer);
+  this.transformer       = this.normalise(transformer);
   this.optional          = !!transformer.optional;
   this.opts              = opts || {};
   this.key               = key;
 }
 
-Transformer.normalise = function (transformer) {
+Transformer.prototype.normalise = function (transformer) {
+  var self = this;
+
   if (_.isFunction(transformer)) {
     transformer = { ast: transformer };
   }
 
   _.each(transformer, function (fns, type) {
     // hidden property
-    if (type[0] === "_") return;
+    if (type[0] === "_") {
+      self[type] = fns;
+      return;
+    }
 
     if (_.isFunction(fns)) fns = { enter: fns };