diff --git a/lib/querystring.js b/lib/querystring.js
index aa433982a6f..0effe5b1679 100644
--- a/lib/querystring.js
+++ b/lib/querystring.js
@@ -166,7 +166,7 @@ QueryString.parse = QueryString.decode = function(qs, sep, eq) {
     var k = QueryString.unescape(x[0], true);
     var v = QueryString.unescape(x.slice(1).join(eq), true);
 
-    if (!(k in obj)) {
+    if (!obj.hasOwnProperty(k)) {
       obj[k] = v;
     } else if (!Array.isArray(obj[k])) {
       obj[k] = [obj[k], v];
diff --git a/test/simple/test-querystring.js b/test/simple/test-querystring.js
index 8e30dae1e5a..18d06422a1e 100644
--- a/test/simple/test-querystring.js
+++ b/test/simple/test-querystring.js
@@ -48,7 +48,12 @@ var qsTestCases = [
      'undef': ''}],
   [' foo = bar ', '%20foo%20=%20bar%20', {' foo ': ' bar '}],
   ['foo=%zx', 'foo=%25zx', {'foo': '%zx'}],
-  ['foo=%EF%BF%BD', 'foo=%EF%BF%BD', {'foo': '\ufffd' }]
+  ['foo=%EF%BF%BD', 'foo=%EF%BF%BD', {'foo': '\ufffd' }],
+  [ 'toString=foo&valueOf=bar&__defineGetter__=baz',
+    'toString=foo&valueOf=bar&__defineGetter__=baz',
+    { toString: 'foo',
+      valueOf: 'bar',
+      __defineGetter__: 'baz' } ]
 ];
 
 // [ wonkyQS, canonicalQS, obj ]