diff --git a/lib/6to5/transformer.js b/lib/6to5/transformer.js
index 59f340efdc..3e05ccd166 100644
--- a/lib/6to5/transformer.js
+++ b/lib/6to5/transformer.js
@@ -28,9 +28,13 @@ Transformer.prototype.transform = function (file) {
   var transformer = this.transformer;
   var ast         = file.ast;
 
-  if (transformer.ast && transformer.ast.enter) {
-    transformer.ast.enter(ast, file);
-  }
+  var astRun = function (key) {
+    if (transformer.ast && transformer.ast[key]) {
+      transformer.ast[key](ast, file);
+    }
+  };
+
+  astRun("enter");
 
   var build = function (exit) {
     return function (node, parent, opts) {
@@ -59,9 +63,7 @@ Transformer.prototype.transform = function (file) {
     exit:  build(true)
   });
 
-  if (transformer.ast && transformer.ast.exit) {
-    transformer.ast.exit(ast, file);
-  }
+  astRun("exit");
 };
 
 Transformer.prototype.canRun = function (file) {