diff --git a/lib/6to5/transformers/array-comprehension.js b/lib/6to5/transformers/array-comprehension.js
index cf553a688d..f7ba4ba315 100644
--- a/lib/6to5/transformers/array-comprehension.js
+++ b/lib/6to5/transformers/array-comprehension.js
@@ -1,29 +1,21 @@
 var util = require("../util");
 var _    = require("lodash");
 
-exports.ComprehensionExpression = function (node, parent, opts, generateUid) {
-  var blocks = node.blocks;
+var single = function (node) {
+  var block = node.blocks[0];
 
-  _.each(blocks, function (block) {
-    if (!block.of) {
-      throw util.errorWithNode(block, "for-in array comprehension is not supported");
-    }
+  var templateName = "array-comprehension-map";
+  if (node.filter) templateName = "array-comprehension-filter";
+
+  return util.template(templateName, {
+    STATEMENT: node.body,
+    FILTER:    node.filter,
+    ARRAY:     block.right,
+    KEY:       block.left
   });
+};
 
-  if (blocks.length === 1) {
-    var block = blocks[0];
-
-    var templateName = "array-comprehension-map";
-    if (node.filter) templateName += "-filter";
-
-    return util.template(templateName, {
-      ARRAY: block.right,
-      KEY: block.left,
-      FILTER: node.filter,
-      STATEMENT: node.body
-    });
-  }
-
+var multiple = function (node, generateUid) {
   var uid = generateUid("arr");
 
   var container = util.template("array-comprehension-container", {
@@ -36,7 +28,7 @@ exports.ComprehensionExpression = function (node, parent, opts, generateUid) {
   var returnStatement = body.pop();
 
   var build = function () {
-    var self = blocks.shift();
+    var self = node.blocks.shift();
     if (!self) return;
 
     var child = build();
@@ -44,8 +36,8 @@ exports.ComprehensionExpression = function (node, parent, opts, generateUid) {
       // last item
 
       child = util.template("array-push", {
-        KEY: uid,
-        STATEMENT: node.body
+        STATEMENT: node.body,
+        KEY:       uid
       }, true);
 
       // add a filter as this is our final stop
@@ -60,7 +52,7 @@ exports.ComprehensionExpression = function (node, parent, opts, generateUid) {
 
     var container2 = util.template("array-comprehension-for-each", {
       ARRAY: self.right,
-      KEY: self.left
+      KEY:   self.left
     }, true);
     container2.expression.arguments[0].body.body = [child];
     return container2;
@@ -71,3 +63,17 @@ exports.ComprehensionExpression = function (node, parent, opts, generateUid) {
 
   return container;
 };
+
+exports.ComprehensionExpression = function (node, parent, opts, generateUid) {
+  _.each(node.blocks, function (block) {
+    if (!block.of) {
+      throw util.errorWithNode(block, "for-in array comprehension is not supported");
+    }
+  });
+
+  if (node.blocks.length === 1) {
+    return single(node);
+  } else {
+    return multiple(node, generateUid);
+  }
+};
diff --git a/lib/6to5/transformers/arrow-functions.js b/lib/6to5/transformers/arrow-functions.js
index 558cd8388d..bf91af9915 100644
--- a/lib/6to5/transformers/arrow-functions.js
+++ b/lib/6to5/transformers/arrow-functions.js
@@ -1,18 +1,15 @@
 var traverse = require("../traverse");
 var util     = require("../util");
+var b        = require("ast-types").builders;
 
 exports.ArrowFunctionExpression = function (node) {
   var body = node.body;
 
   // expression body
   if (body.type !== "BlockStatement") {
-    body = {
-      type: "BlockStatement",
-      body: [{
-        type: "ReturnStatement",
-        argument: body
-      }]
-    };
+    body = b.blockStatement([
+      b.returnStatement(body)
+    ]);
   }
 
   node.expression = false;
diff --git a/lib/6to5/transformers/block-binding.js b/lib/6to5/transformers/block-binding.js
index ee53ae3a38..ca7104dae1 100644
--- a/lib/6to5/transformers/block-binding.js
+++ b/lib/6to5/transformers/block-binding.js
@@ -1,9 +1,10 @@
 var traverse = require("../traverse");
 var util     = require("../util");
+var b        = require("ast-types").builders;
 var _        = require("lodash");
 
 var isLet = function (node) {
-  if (node.type === "VariableDeclaration" && node.kind === "let") {
+  if (node && node.type === "VariableDeclaration" && node.kind === "let") {
     node.kind = "var";
     node._ignoreBlockBindingHoist = true;
     return true;
@@ -54,16 +55,14 @@ var buildNode = function (node) {
     if (node._ignoreBlockBindingHoist) return node;
 
     if (node.type === "VariableDeclaration" && node.kind === "var") {
-      _.each(node.declarations, function (declar) {
-        nodes.push(util.template("variable-declare", {
-          KEY: declar.id
-        }));
-      });
+      nodes.push(b.variableDeclaration("var", node.declarations.map(function (declar) {
+        return b.variableDeclarator(declar.id, null);
+      })));
 
       return node.declarations.map(function (declar) {
         return util.template("assign", {
-          KEY: declar.id,
-          VALUE: declar.init
+          VALUE: declar.init,
+          KEY:   declar.id
         }, true);
       });
     } else if (node.type === "ForInStatement" && !node.left._ignoreBlockBindingHoist) {
@@ -79,15 +78,9 @@ var buildNode = function (node) {
 
   //
 
-  var func = {
-    type: "FunctionExpression",
-    params: [],
-    defaults: [],
-    body: {
-      type: "BlockStatement",
-      body: node
-    }
-  };
+  var block = b.blockStatement([]);
+  block.body = node;
+  var func = b.functionExpression(null, [], block, false)
 
   var templateName = "function-call";
   if (traverse.hasType(node, "ThisExpression")) {
diff --git a/lib/6to5/transformers/classes.js b/lib/6to5/transformers/classes.js
index 08163a1681..f42c0e09cd 100644
--- a/lib/6to5/transformers/classes.js
+++ b/lib/6to5/transformers/classes.js
@@ -1,5 +1,6 @@
 var traverse = require("../traverse");
 var util     = require("../util");
+var b        = require("ast-types").builders;
 var _        = require("lodash");
 
 exports.ClassDeclaration = function (node) {
@@ -47,7 +48,7 @@ var buildClassBody = function (body, className, superName, node) {
       if (node.kind === "") {
         addConstructor(body[0], method);
       } else {
-        throw new Error("unknown kind for constructor method");
+        throw util.errorWithNode(node, "unknown kind for constructor method");
       }
     } else {
       if (node.kind === "") {
@@ -69,29 +70,27 @@ var buildClassBody = function (body, className, superName, node) {
 
 var superIdentifier = function (superName, node, parent) {
   if (parent.property === node) return;
-  if (!superName) return;
 
-  node.name = superName.name;
+  node.name = superName.name || superName.value;
 
   // super(); -> ClassName.call(this);
   if (parent.type === "CallExpression" && parent.callee === node) {
     node.name += ".call";
-    parent.arguments.unshift({
-      type: "ThisExpression"
-    });
+    parent.arguments.unshift(b.thisExpression());
   }
 };
 
 var replaceInstanceSuperReferences = function (superName, method) {
+  superName = superName || b.literal("Function");
+
   traverse(method, function (node, parent) {
     if (node.type === "Identifier" && node.name === "super") {
       superIdentifier(superName, node, parent);
     } else if (node.type === "MemberExpression") {
       // no accessing of super properties
 
-
       if (isAccessingSuperProperties(parent, node)) {
-        throw new Error("cannot access super properties");
+        throw util.errorWithNode(node, "cannot access super properties");
       } else {
         return;
       }
@@ -101,16 +100,10 @@ var replaceInstanceSuperReferences = function (superName, method) {
       if (callee.object.name !== "super") return;
 
       callee.property.name = "prototype." + callee.property.name + ".call";
-      node.arguments.unshift({
-        type: "ThisExpression"
-      });
+      node.arguments.unshift(b.thisExpression());
     } else {
       return;
     }
-
-    if (!superName) {
-      throw new Error("cannot access super as this class has none");
-    }
   });
 };
 
diff --git a/lib/6to5/transformers/default-parameters.js b/lib/6to5/transformers/default-parameters.js
index aaf8bdc024..7ecf39c72f 100644
--- a/lib/6to5/transformers/default-parameters.js
+++ b/lib/6to5/transformers/default-parameters.js
@@ -1,6 +1,7 @@
 var util = require("../util");
 var _    = require("lodash");
 
+exports.FunctionDeclaration =
 exports.FunctionExpression = function (node) {
   _.each(node.defaults, function (def, i) {
     if (!def) return;
diff --git a/lib/6to5/transformers/destructuring.js b/lib/6to5/transformers/destructuring.js
index db58ddb879..bb6e714e17 100644
--- a/lib/6to5/transformers/destructuring.js
+++ b/lib/6to5/transformers/destructuring.js
@@ -1,4 +1,5 @@
 var util = require("../util");
+var b    = require("ast-types").builders;
 var _    = require("lodash");
 
 var isPattern = function (id) {
@@ -20,15 +21,9 @@ exports.VariableDeclaration = function (node, parent, opts, generateUid) {
   //
 
   var buildVariableAssign = function (id, init) {
-    return {
-      type: "VariableDeclaration",
-      kind: node.kind,
-      declarations: [{
-        type: "VariableDeclarator",
-        id: id,
-        init: init
-      }]
-    };
+    return b.variableDeclaration(node.kind, [
+      b.variableDeclarator(id, init)
+    ]);
   };
 
   var push = function (pattern, parentId) {
@@ -43,11 +38,7 @@ exports.VariableDeclaration = function (node, parent, opts, generateUid) {
     _.each(pattern.properties, function (prop) {
       var id = prop.value;
 
-      var init = {
-        type: "MemberExpression",
-        object: parentId,
-        property: prop.key
-      };
+      var init = b.memberExpression(parentId, prop.key, false);
 
       if (isPattern(id)) {
         push(id, init);
@@ -59,15 +50,7 @@ exports.VariableDeclaration = function (node, parent, opts, generateUid) {
 
   var pushArrayPattern = function (pattern, parentId) {
     _.each(pattern.elements, function (id, i) {
-      var init = {
-        type: "MemberExpression",
-        computed: true,
-        object: parentId,
-        property: {
-          type: "Literal",
-          value: i
-        }
-      };
+      var init = b.memberExpression(parentId, b.literal(i), true);
 
       if (id.type === "Identifier") {
         nodes.push(buildVariableAssign(id, init));
@@ -86,10 +69,7 @@ exports.VariableDeclaration = function (node, parent, opts, generateUid) {
         VALUE: init
       }, true));
 
-      init = {
-        type: "Identifier",
-        name: key
-      };
+      init = b.identifier(key);
     }
 
     push(id, init);
diff --git a/lib/6to5/transformers/for-of.js b/lib/6to5/transformers/for-of.js
index b1ac7426ea..8b18294647 100644
--- a/lib/6to5/transformers/for-of.js
+++ b/lib/6to5/transformers/for-of.js
@@ -3,18 +3,16 @@ var util = require("../util");
 exports.ForOfStatement = function (node, parent, opts, generateUid) {
   var node2 = util.template("for-of", {
     ITERATOR_KEY: generateUid("iterator"),
-    STEP_KEY: generateUid("step"),
-
-    KEY: node.left.declarations[0].id,
-    OBJECT: node.right
+    STEP_KEY:     generateUid("step"),
+    OBJECT:       node.right,
+    KEY:          node.left.declarations[0].id
   });
 
-  var block = node2.body;
-
-  var declar = block.body[0];
-  declar.kind = node.left.kind;
-
+  var block  = node2.body;
   block.body = block.body.concat(node.body.body);
 
+  var declar  = block.body[0];
+  declar.kind = node.left.kind;
+
   return node2;
 };
diff --git a/lib/6to5/transformers/modules.js b/lib/6to5/transformers/modules.js
index 3dfda826d1..be4b1b4c93 100644
--- a/lib/6to5/transformers/modules.js
+++ b/lib/6to5/transformers/modules.js
@@ -1,4 +1,5 @@
 var util = require("../util");
+var b    = require("ast-types").builders;
 var _    = require("lodash");
 
 exports.ImportDeclaration = function (node) {
@@ -35,15 +36,22 @@ exports.ExportDeclaration = function (node) {
   _.each(node.specifiers, function (specifier) {
     var variableName = specifier.name || specifier.id;
 
-    if (specifier.type === "ExportBatchSpecifier") {
-      nodes.push(util.template("exports-wildcard", {
-        MODULE_NAME: node.source
-      }, true));
+    if (node.source) {
+      if (specifier.type === "ExportBatchSpecifier") {
+        nodes.push(util.template("exports-wildcard", {
+          MODULE_NAME: node.source
+        }, true));
+      } else {
+        nodes.push(util.template("exports-require-assign-key", {
+          VARIABLE_NAME: variableName.name,
+          MODULE_NAME:   node.source,
+          KEY:           specifier.id
+        }, true));
+      }
     } else {
-      nodes.push(util.template("exports-require-assign-key", {
-        VARIABLE_NAME: variableName.name,
-        MODULE_NAME:   node.source,
-        KEY:           specifier.id.name
+      nodes.push(util.template("exports-assign", {
+        VALUE: specifier.id,
+        KEY:   specifier.id
       }, true));
     }
   });
@@ -61,10 +69,7 @@ exports.ExportDeclaration = function (node) {
 
         _.each(declar.declarations, function (declar) {
           nodes.push(util.template("exports-alias-var", {
-            STRING_KEY: {
-              type: "Literal",
-              value: declar.id.name
-            },
+            STRING_KEY: b.literal(declar.id.name),
             KEY: declar.id
           }, true));
         });
diff --git a/lib/6to5/transformers/property-method-assignment.js b/lib/6to5/transformers/property-method-assignment.js
index 90a1386d3d..8ed7f130f2 100644
--- a/lib/6to5/transformers/property-method-assignment.js
+++ b/lib/6to5/transformers/property-method-assignment.js
@@ -1,4 +1,5 @@
 var util = require("../util");
+var b    = require("ast-types").builders;
 var _    = require("lodash");
 
 exports.Property = function (node) {
@@ -6,9 +7,6 @@ exports.Property = function (node) {
 };
 
 exports.ObjectExpression = function (node) {
-  //if (node.ignorePropertyMethods) return;
-  //node.ignorePropertyMethods = true;
-
   var mutatorMap = {};
 
   node.properties = node.properties.filter(function (prop) {
@@ -24,9 +22,6 @@ exports.ObjectExpression = function (node) {
 
   return util.template("object-define-properties-closure", {
     OBJECT: node,
-    CONTENT: util.buildDefineProperties(mutatorMap, {
-      type: "Identifier",
-      name: "obj"
-    }).expression
+    CONTENT: util.buildDefineProperties(mutatorMap, b.identifier("obj")).expression
   });
 };
diff --git a/lib/6to5/transformers/rest-parameters.js b/lib/6to5/transformers/rest-parameters.js
index ee229e3d6c..85b5e4cdad 100644
--- a/lib/6to5/transformers/rest-parameters.js
+++ b/lib/6to5/transformers/rest-parameters.js
@@ -1,5 +1,7 @@
 var util = require("../util");
+var b    = require("ast-types").builders;
 
+exports.FunctionDeclaration =
 exports.FunctionExpression = function (node) {
   if (!node.rest) return;
 
@@ -11,9 +13,6 @@ exports.FunctionExpression = function (node) {
 
   node.body.body.unshift(util.template(templateName, {
     VARIABLE_NAME: rest,
-    SLICE_ARG: {
-      type: "Literal",
-      value: node.params.length
-    }
+    SLICE_ARG: b.literal(node.params.length)
   }));
 };
diff --git a/lib/6to5/transformers/spread.js b/lib/6to5/transformers/spread.js
index dea623d8a1..ee8e1a2c4a 100644
--- a/lib/6to5/transformers/spread.js
+++ b/lib/6to5/transformers/spread.js
@@ -1,4 +1,5 @@
 var util = require("../util");
+var b    = require("ast-types").builders;
 var _    = require("lodash");
 
 exports.ArrayExpression = function (node) {
@@ -28,12 +29,8 @@ exports.CallExpression = function (node) {
   if (args.length && _.last(args).type === "SpreadElement") {
     var spread = args.pop();
 
-    var spreadLiteral = spread.argument;
-
-    var contextLiteral = {
-      type: "Literal",
-      value: null
-    };
+    var spreadLiteral  = spread.argument;
+    var contextLiteral = b.literal(null);
 
     node.arguments = [];
 
diff --git a/lib/6to5/transformers/template-literals.js b/lib/6to5/transformers/template-literals.js
index 37e5feb75a..bd42449c09 100644
--- a/lib/6to5/transformers/template-literals.js
+++ b/lib/6to5/transformers/template-literals.js
@@ -1,22 +1,15 @@
+var b = require("ast-types").builders;
 var _ = require("lodash");
 
 var buildBinaryExpression = function (left, right) {
-  return {
-    type: "BinaryExpression",
-    operator: "+",
-    left: left,
-    right: right
-  };
+  return b.binaryExpression("+", left, right);
 };
 
 exports.TemplateLiteral = function (node) {
   var nodes = [];
 
   _.each(node.quasis, function (elem) {
-    nodes.push({
-      type: "Literal",
-      value: elem.value.raw
-    });
+    nodes.push(b.literal(elem.value.raw));
 
     var expr = node.expressions.shift();
     if (expr) nodes.push(expr);