diff --git a/lib/6to5/transformation/transformers/optional-core-aliasing.js b/lib/6to5/transformation/transformers/optional-core-aliasing.js
index 28bd850193..15961756c3 100644
--- a/lib/6to5/transformation/transformers/optional-core-aliasing.js
+++ b/lib/6to5/transformation/transformers/optional-core-aliasing.js
@@ -17,10 +17,12 @@ exports.ast = {
   exit: function (ast, file) {
     traverse(ast, {
       enter: function (node, parent) {
-        if (t.isMemberExpression(node)) {
+        var prop;
+
+        if (t.isMemberExpression(node) && t.isReferenced(node, parent)) {
           // Array.from -> _core.Array.from
-          var obj  = node.object;
-          var prop = node.property;
+          var obj = node.object;
+          prop = node.property;
 
           if (!t.isReferenced(obj, node)) return;
 
@@ -38,7 +40,7 @@ exports.ast = {
           if (!t.isMemberExpression(callee)) return;
           if (!callee.computed) return;
 
-          var prop = callee.property;
+          prop = callee.property;
           if (!t.isIdentifier(prop.object, { name: "Symbol" })) return;
           if (!t.isIdentifier(prop.property, { name: "iterator" })) return;
 
diff --git a/lib/6to5/transformation/transformers/playground-object-getter-memoization.js b/lib/6to5/transformation/transformers/playground-object-getter-memoization.js
index c2866e00f8..5d05abe82c 100644
--- a/lib/6to5/transformation/transformers/playground-object-getter-memoization.js
+++ b/lib/6to5/transformation/transformers/playground-object-getter-memoization.js
@@ -3,15 +3,14 @@ var util     = require("../../util");
 var t        = require("../../types");
 
 exports.Property =
-exports.MethodDefinition = function (node, parent, file, scope) {
+exports.MethodDefinition = function (node) {
   if (node.kind !== "memo") return;
   node.kind = "get";
 
   var value = node.value;
   t.ensureBlock(value);
 
-  var body  = value.body.body;
-  var key   = node.key;
+  var key = node.key;
 
   if (t.isIdentifier(key) && !node.computed) {
     key = t.literal(key.name);