diff --git a/lib/6to5/transformation/transformers/_alias-functions.js b/lib/6to5/transformation/transformers/_alias-functions.js
index 4d4b78ea67..7dbabf3710 100644
--- a/lib/6to5/transformation/transformers/_alias-functions.js
+++ b/lib/6to5/transformation/transformers/_alias-functions.js
@@ -20,7 +20,7 @@ var go = function (getBody, node, file, scope) {
       if (!node._aliasFunction) {
         if (t.isFunction(node)) {
           // stop traversal of this node as it'll be hit again by this transformer
-          return false;
+          return this.stop();
         } else {
           return;
         }
@@ -30,10 +30,10 @@ var go = function (getBody, node, file, scope) {
       traverse(node, {
         enter: function (node, parent) {
           if (t.isFunction(node) && !node._aliasFunction) {
-            return false;
+            return this.stop();
           }
 
-          if (node._ignoreAliasFunctions) return false;
+          if (node._ignoreAliasFunctions) return this.stop();
 
           var getId;
 
@@ -49,7 +49,7 @@ var go = function (getBody, node, file, scope) {
         }
       });
 
-      return false;
+      return this.stop();
     }
   });
 
diff --git a/lib/6to5/transformation/transformers/es6-generators.js b/lib/6to5/transformation/transformers/es6-generators.js
index 7b7c0a3f0e..c7dc28d55e 100644
--- a/lib/6to5/transformation/transformers/es6-generators.js
+++ b/lib/6to5/transformation/transformers/es6-generators.js
@@ -1 +1,3 @@
-module.exports = require("regenerator").transform;
+exports.ast = {
+  before: require("regenerator").transform
+};
diff --git a/lib/6to5/transformation/transformers/es6-let-scoping.js b/lib/6to5/transformation/transformers/es6-let-scoping.js
index 7d6fa09b76..3abc6c6c90 100644
--- a/lib/6to5/transformation/transformers/es6-let-scoping.js
+++ b/lib/6to5/transformation/transformers/es6-let-scoping.js
@@ -280,7 +280,7 @@ LetScoping.prototype.checkLoop = function () {
       var replace;
 
       if (t.isFunction(node) || t.isLoop(node)) {
-        return false;
+        return this.stop();
       }
 
       if (node && !node.label) {
@@ -329,7 +329,7 @@ LetScoping.prototype.hoistVarDeclarations = function () {
       } else if (isVar(node, parent)) {
         return self.pushDeclar(node).map(t.expressionStatement);
       } else if (t.isFunction(node)) {
-        return false;
+        return this.stop();
       }
     }
   });
@@ -388,9 +388,9 @@ LetScoping.prototype.getLetReferences = function () {
           }
         });
 
-        return false;
+        return this.stop();
       } else if (t.isLoop(node)) {
-        return false;
+        return this.stop();
       }
     }
   });
diff --git a/lib/6to5/transformation/transformers/use-strict.js b/lib/6to5/transformation/transformers/use-strict.js
index c4b352cc20..02d4dbc264 100644
--- a/lib/6to5/transformation/transformers/use-strict.js
+++ b/lib/6to5/transformation/transformers/use-strict.js
@@ -1,12 +1,14 @@
 var t = require("../../types");
 
-module.exports = function (ast) {
-  var body = ast.program.body;
-  var first = body[0];
+exports.ast = {
+  exit: function (ast) {
+    var body = ast.program.body;
+    var first = body[0];
 
-  var noStrict = !first || !t.isExpressionStatement(first) || !t.isLiteral(first.expression) || first.expression.value !== "use strict";
+    var noStrict = !first || !t.isExpressionStatement(first) || !t.isLiteral(first.expression) || first.expression.value !== "use strict";
 
-  if (noStrict) {
-    body.unshift(t.expressionStatement(t.literal("use strict")));
+    if (noStrict) {
+      body.unshift(t.expressionStatement(t.literal("use strict")));
+    }
   }
 };