diff --git a/lib/6to5/util.js b/lib/6to5/util.js
index 04ced6f323..36ca58e3d3 100644
--- a/lib/6to5/util.js
+++ b/lib/6to5/util.js
@@ -58,7 +58,16 @@ exports.sourceMapToComment = function (map) {
 };
 
 exports.pushMutatorMap = function (mutatorMap, key, kind, method) {
-  var alias = JSON.stringify(traverse.removeProperties(_.cloneDeep(key)));
+  var alias;
+
+  if (t.isIdentifier(key)) {
+    alias = key.name;
+    if (method.computed) alias = "computed:" + alias;
+  } else if (t.isLiteral(key)) {
+    alias = String(key.value);
+  } else {
+    alias = JSON.stringify(traverse.removeProperties(_.cloneDeep(key)));
+  }
 
   var map;
   if (_.has(mutatorMap, alias)) {
@@ -174,7 +183,7 @@ exports.parse = function (opts, code, callback) {
       ecmaVersion: Infinity,
       strictMode:  true,
       onComment:   comments,
-      locations:   opts.sourceMap,
+      locations:   true,
       onToken:     tokens,
       ranges:      true
     });