diff --git a/lib/6to5/types/builder-keys.json b/lib/6to5/types/builder-keys.json
index 98e5e24800..52aa00845e 100644
--- a/lib/6to5/types/builder-keys.json
+++ b/lib/6to5/types/builder-keys.json
@@ -1,33 +1,162 @@
 {
-  "ArrayExpression":         ["elements"],
-  "ArrowFunctionExpression": ["params", "body"],
-  "AssignmentExpression":    ["operator", "left", "right"],
-  "BinaryExpression":        ["operator", "left", "right"],
-  "BlockStatement":          ["body"],
-  "CallExpression":          ["callee", "arguments"],
-  "ConditionalExpression":   ["test", "consequent", "alternate"],
-  "ExpressionStatement":     ["expression"],
-  "File":                    ["program", "comments", "tokens"],
-  "FunctionExpression":      ["id", "params", "body", "generator"],
-  "FunctionDeclaration":     ["id", "params", "body", "generator"],
-  "Identifier":              ["name"],
-  "IfStatement":             ["test", "consequent", "alternate"],
-  "ImportDeclaration":       ["specifiers", "source"],
-  "ImportSpecifier":         ["id", "name"],
-  "Literal":                 ["value"],
-  "LogicalExpression":       ["operator", "left", "right"],
-  "MemberExpression":        ["object", "property", "computed"],
-  "MethodDefinition":        ["key", "value", "computed", "kind"],
-  "NewExpression":           ["callee", "arguments"],
-  "ObjectExpression":        ["properties"],
-  "Program":                 ["body"],
-  "Property":                ["kind", "key", "value", "computed"],
-  "ReturnStatement":         ["argument"],
-  "SequenceExpression":      ["expressions"],
-  "ThrowExpression":         ["argument"],
-  "UnaryExpression":         ["operator", "argument", "prefix"],
-  "VariableDeclaration":     ["kind", "declarations"],
-  "VariableDeclarator":      ["id", "init"],
-  "WithStatement":           ["object", "body"],
-  "YieldExpression":         ["argument", "delegate"]
+  "ArrayExpression": {
+    "elements": null
+  },
+
+  "ArrowFunctionExpression": {
+    "params": null,
+    "body": null
+  },
+
+  "AssignmentExpression": {
+    "operator": null,
+    "left": null,
+    "right": null
+  },
+
+  "BinaryExpression": {
+    "operator": null,
+    "left": null,
+    "right": null
+  },
+
+  "BlockStatement": {
+    "body": null
+  },
+
+  "CallExpression": {
+    "callee": null,
+    "arguments": null
+  },
+
+  "ConditionalExpression": {
+    "test": null,
+    "consequent": null,
+    "alternate": null
+  },
+
+  "ExpressionStatement": {
+    "expression": null
+  },
+
+  "File": {
+    "program": null,
+    "comments": null,
+    "tokens": null
+  },
+
+  "FunctionExpression": {
+    "id": null,
+    "params": null,
+    "body": null,
+    "generator": false
+  },
+
+  "FunctionDeclaration": {
+    "id": null,
+    "params": null,
+    "body": null,
+    "generator": false
+  },
+
+  "Identifier": {
+    "name": null
+  },
+
+  "IfStatement": {
+    "test": null,
+    "consequent": null,
+    "alternate": null
+  },
+
+  "ImportDeclaration": {
+    "specifiers": null,
+    "source": null
+  },
+
+  "ImportSpecifier": {
+    "id": null,
+    "name": null
+  },
+
+  "Literal": {
+    "value": null
+  },
+
+  "LogicalExpression": {
+    "operator": null,
+    "left": null,
+    "right": null
+  },
+
+  "MemberExpression": {
+    "object": null,
+    "property": null,
+    "computed": false
+  },
+
+  "MethodDefinition": {
+    "key": null,
+    "value": null,
+    "computed": false,
+    "kind": null
+  },
+
+  "NewExpression": {
+    "callee": null,
+    "arguments": null
+  },
+
+  "ObjectExpression": {
+    "properties": null
+  },
+
+  "Program": {
+    "body": null
+  },
+
+  "Property": {
+    "kind": null,
+    "key": null,
+    "value": null,
+    "computed": false
+  },
+
+  "ReturnStatement": {
+    "argument": null
+  },
+
+  "SequenceExpression": {
+    "expressions": null
+  },
+
+  "ThrowExpression": {
+    "argument": null
+  },
+
+  "UnaryExpression": {
+    "operator": null,
+    "argument": null,
+    "prefix": null
+  },
+
+  "VariableDeclaration": {
+    "kind": null,
+    "declarations": null
+  },
+
+  "VariableDeclarator": {
+    "id": null,
+    "init": null
+  },
+
+  "WithStatement": {
+    "object": null,
+    "body": null
+  },
+
+  "YieldExpression": {
+    "argument": null,
+    "delegate": null
+  }
 }
diff --git a/lib/6to5/types/index.js b/lib/6to5/types/index.js
index 0b90c56175..fb3a871b92 100644
--- a/lib/6to5/types/index.js
+++ b/lib/6to5/types/index.js
@@ -97,20 +97,29 @@ t.is = function (type, node, opts, skipAliasCheck) {
 
 //
 
-t.BUILDER_KEYS = defaults(require("./builder-keys"), t.VISITOR_KEYS);
+t.BUILDER_KEYS = require("./builder-keys");
+
+each(t.VISITOR_KEYS, function (keys, type) {
+  if (t.BUILDER_KEYS[type]) return;
+
+  var defs = {};
+  each(keys, function (key) {
+    defs[key] = null;
+  });
+  t.BUILDER_KEYS[type] = defs;
+});
 
 each(t.BUILDER_KEYS, function (keys, type) {
   t[type[0].toLowerCase() + type.slice(1)] = function () {
-    var args = arguments;
     var node = new Node;
     node.start = null;
     node.type = type;
 
-    for (var i = 0; i < keys.length; i++) {
-      var arg = args[i];
-      if (arg === undefined) arg = false;
+    var i = 0;
 
-      var key = keys[i];
+    for (var key in keys) {
+      var arg = arguments[i++];
+      if (arg === undefined) arg = keys[key];
       node[key] = arg;
     }