diff --git a/lib/util.js b/lib/util.js
index 823b6f051f04..4bf0e8a7b555 100644
--- a/lib/util.js
+++ b/lib/util.js
@@ -744,17 +744,16 @@ exports._errnoException = function(err, syscall, original, additions) {
   e.errno = errname;
   e.syscall = syscall;
   if (additions && isObject(additions)) {
-    var add = exports._extend(e, additions);
-    var keys = Object.keys(add);
-    var i = keys.length;
-    while (i--) {
-      var key = keys[i];
-      var val = add[key];
-      if (isNullOrUndefined(val) || isFunction(val)) {
-        delete add[key];
+    var keys = Object.keys(additions);
+    var len = keys.length;
+    for (var i = 0; i < len; i++) {
+      if (isNullOrUndefined(keys[i]) || isFunction(keys[i])) {
+        delete additions[keys[i]];
+        keys.splice(i, 1);
+        i--;
       }
     }
-    e = add;
+    exports._extend(e, additions);
   }
   return e;
 };