diff --git a/src/json.js b/src/json.js
index cdb10be1aa..e7ec6100e5 100644
--- a/src/json.js
+++ b/src/json.js
@@ -29,7 +29,7 @@ var $JSON = global.JSON;
 
 function ParseJSONUnfiltered(text) {
   var s = $String(text);
-  var f = %CompileString(text, true);
+  var f = %CompileString(s, true);
   return f();
 }
 
diff --git a/test/mjsunit/json.js b/test/mjsunit/json.js
index 85457cd6e1..945b66249b 100644
--- a/test/mjsunit/json.js
+++ b/test/mjsunit/json.js
@@ -85,7 +85,7 @@ n4.toISOString = function () {
 };
 assertEquals(null, n4.toJSON());
 
-assertEquals(Object.prototype, JSON.__proto__);
+assertTrue(Object.prototype === JSON.__proto__);
 assertEquals("[object JSON]", Object.prototype.toString.call(JSON));
 
 // DontEnum
@@ -313,3 +313,7 @@ TestInvalid('1); throw "foo"; (1');
 var x = 0;
 eval("(1); x++; (1)");
 TestInvalid('1); x++; (1');
+
+// Test string conversion of argument.
+var o = { toString: function() { return "42"; } };
+assertEquals(42, JSON.parse(o));