diff -r 3fbfa61634de Lib/json/decoder.py
--- a/Lib/json/decoder.py	Thu Jul 19 00:14:35 2012 -0500
+++ b/Lib/json/decoder.py	Fri Jul 20 15:25:15 2012 +0300
@@ -359,13 +359,16 @@
         """Decode a JSON document from ``s`` (a ``str`` beginning with
         a JSON document) and return a 2-tuple of the Python
         representation and the index in ``s`` where the document ended.
+        Optionally, ``idx`` can be used to specify an offset in ``s``
+        where the document begins.
 
         This can be used to decode a JSON document from a string that may
         have extraneous data at the end.
 
         """
+        _w = WHITESPACE.match
         try:
-            obj, end = self.scan_once(s, idx)
+            obj, end = self.scan_once(s, idx=_w(s, idx).end())
         except StopIteration:
             raise ValueError("No JSON object could be decoded")
         return obj, end
diff -r 3fbfa61634de Lib/test/json_tests/test_decode.py
--- a/Lib/test/json_tests/test_decode.py	Thu Jul 19 00:14:35 2012 -0500
+++ b/Lib/test/json_tests/test_decode.py	Fri Jul 20 15:25:15 2012 +0300
@@ -55,5 +55,21 @@
         self.check_keys_reuse(s, self.json.decoder.JSONDecoder().decode)
 
 
+class TestRawDecode:
+    def test_whitespace(self):
+        decoder = self.json.JSONDecoder()
+        self.assertEqual(decoder.raw_decode(' {}'), ({}, 3))
+        self.assertEqual(decoder.raw_decode('  []'), ([], 4))
+        self.assertEqual(decoder.raw_decode('   ""'), ('', 5))
+        s = '  {   "key"    :    "value"    ,  "k":"v"    } \n' \
+            ' { "key": "value",  "k" :"v"} '
+        val1, n1 = decoder.raw_decode(s)
+        val2, n2 = decoder.raw_decode(s[n1:])
+        self.assertEqual(val1, {"key":"value", "k":"v"})
+        self.assertEqual(val2, {"key":"value", "k":"v"})
+
+
 class TestPyDecode(TestDecode, PyTest): pass
 class TestCDecode(TestDecode, CTest): pass
+class TestPyRawDecode(TestRawDecode, PyTest): pass
+class TestCRawDecode(TestRawDecode, CTest): pass