diff --git a/lib/6to5/transformation/transformers/es6-default-parameters.js b/lib/6to5/transformation/transformers/es6-default-parameters.js
index eb7b6fc1b3..db82d8e2d4 100644
--- a/lib/6to5/transformation/transformers/es6-default-parameters.js
+++ b/lib/6to5/transformation/transformers/es6-default-parameters.js
@@ -1,7 +1,6 @@
 var traverse = require("../../traverse");
 var util     = require("../../util");
 var t        = require("../../types");
-var _        = require("lodash");
 
 exports.Function = function (node, parent, file, scope) {
   if (!node.defaults || !node.defaults.length) return;
@@ -15,6 +14,23 @@ exports.Function = function (node, parent, file, scope) {
   var i;
   var def;
 
+  var checkTDZ = function (ids) {
+    var check = function (node, parent) {
+      if (!t.isIdentifier(node) || !t.isReferenced(node, parent)) return;
+
+      if (ids.indexOf(node.name) >= 0) {
+        throw file.errorWithNode(node, "Temporal dead zone - accessing a variable before it's initialized");
+      }
+
+      if (scope.has(node.name, true)) {
+        iife = true;
+      }
+    };
+
+    check(def, node);
+    traverse(def, { enter: check });
+  };
+
   for (i in node.defaults) {
     def = node.defaults[i];
     if (!def) continue;
@@ -23,22 +39,10 @@ exports.Function = function (node, parent, file, scope) {
 
     // temporal dead zone check - here we prevent accessing of params that
     // are to the right - ie. uninitialized parameters
-    _.each(ids.slice(i), function (ids) {
-      var check = function (node, parent) {
-        if (!t.isIdentifier(node) || !t.isReferenced(node, parent)) return;
-
-        if (ids.indexOf(node.name) >= 0) {
-          throw file.errorWithNode(node, "Temporal dead zone - accessing a variable before it's initialized");
-        }
-
-        if (scope.has(node.name, true)) {
-          iife = true;
-        }
-      };
-
-      check(def, node);
-      traverse(def, { enter: check });
-    });
+    var rightIds = ids.slice(i);
+    for (i in rightIds) {
+      checkTDZ(rightIds[i]);
+    }
 
     // we're accessing a variable that's already defined within this function
     var has = scope.get(param.name);
diff --git a/lib/6to5/transformation/transformers/es6-let-scoping.js b/lib/6to5/transformation/transformers/es6-let-scoping.js
index 44151d58b8..a95c1b3a30 100644
--- a/lib/6to5/transformation/transformers/es6-let-scoping.js
+++ b/lib/6to5/transformation/transformers/es6-let-scoping.js
@@ -250,10 +250,11 @@ LetScoping.prototype.getInfo = function () {
     declar = block.body[i];
     if (!isLet(declar, block)) continue;
 
-    _.each(t.getIds(declar, true), function (id, key) {
-      duplicates(id, key);
+    var declars = t.getIds(declar, true);
+    for (var key in declars) {
+      duplicates(declars[key], key);
       opts.keys.push(key);
-    });
+    }
   }
 
   return opts;
diff --git a/lib/6to5/transformation/transformers/optional-classes-fast-super.js b/lib/6to5/transformation/transformers/optional-classes-fast-super.js
deleted file mode 100644
index 7f65c08c93..0000000000
--- a/lib/6to5/transformation/transformers/optional-classes-fast-super.js
+++ /dev/null
@@ -1,74 +0,0 @@
-var traverse = require("../../traverse");
-var util     = require("../../util");
-var t        = require("../../types");
-
-exports.optional = true;
-
-exports.Class = function (node) {
-  var superClass = node.superClass || t.identifier("Function");
-
-  var hasConstructor = false;
-  var body = node.body.body;
-
-  for (var i in body) {
-    var methodNode = body[i];
-
-    hasConstructor = hasConstructor || methodNode.key.name === "constructor";
-
-    traverse(methodNode, {
-      enter: function (node, parent) {
-        if (t.isIdentifier(node, { name: "super" })) {
-          return superIdentifier(superClass, methodNode, node, parent);
-        } else if (t.isCallExpression(node)) {
-          var callee = node.callee;
-          if (!t.isMemberExpression(callee)) return;
-          if (callee.object.name !== "super") return;
-
-          // super.test(); -> ClassName.prototype.MethodName.call(this);
-          t.appendToMemberExpression(callee, t.identifier("call"));
-          node.arguments.unshift(t.thisExpression());
-        }
-      }
-    });
-  }
-
-  if (node.superClass && !hasConstructor) {
-    body.unshift(t.methodDefinition(
-      t.identifier("constructor"),
-      util.template("class-super-constructor-call-fast", {
-        SUPER_NAME: superClass
-      })
-    ));
-  }
-};
-
-var superIdentifier = function (superClass, methodNode, id, parent) {
-  var methodName = methodNode.key;
-
-  if (parent.property === id) {
-    return;
-  } else if (t.isCallExpression(parent, { callee: id })) {
-    // super(); -> ClassName.prototype.MethodName.call(this);
-    parent.arguments.unshift(t.thisExpression());
-
-    if (methodName.name === "constructor") {
-      // constructor() { super(); }
-      return t.memberExpression(superClass, t.identifier("call"));
-    } else {
-      id = superClass;
-
-      // foo() { super(); }
-      if (!methodNode.static) {
-        id = t.memberExpression(id, t.identifier("prototype"));
-      }
-
-      id = t.memberExpression(id, methodName, methodNode.computed);
-      return t.memberExpression(id, t.identifier("call"));
-    }
-  } else if (t.isMemberExpression(parent) && !methodNode.static) {
-    // super.test -> ClassName.prototype.test
-    return t.memberExpression(superClass, t.identifier("prototype"));
-  } else {
-    return superClass;
-  }
-};