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	Thu Jul 19 14:37:51 2012 +0300
@@ -343,29 +343,30 @@
         self.memo = {}
         self.scan_once = scanner.make_scanner(self)
 
-
     def decode(self, s, _w=WHITESPACE.match):
         """Return the Python representation of ``s`` (a ``str`` instance
         containing a JSON document).
 
         """
-        obj, end = self.raw_decode(s, idx=_w(s, 0).end())
+        obj, end = self.raw_decode(s)
         end = _w(s, end).end()
         if end != len(s):
             raise ValueError(errmsg("Extra data", s, end, len(s)))
         return obj
 
-    def raw_decode(self, s, idx=0):
+    def raw_decode(self, s, idx=0, _w=WHITESPACE.match):
         """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.
 
         """
         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	Thu Jul 19 14:37:51 2012 +0300
@@ -55,5 +55,14 @@
         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(' []'), ([], 3))
+        self.assertEqual(decoder.raw_decode(' ""'), ("", 3))
+
 class TestPyDecode(TestDecode, PyTest): pass
 class TestCDecode(TestDecode, CTest): pass
+class TestPyRawDecode(TestRawDecode, PyTest): pass
+class TestCRawDecode(TestRawDecode, CTest): pass