diff -r 1267d64c14b3 Lib/json/decoder.py
--- a/Lib/json/decoder.py	Thu Nov 01 14:52:03 2012 +0200
+++ b/Lib/json/decoder.py	Thu Nov 01 23:40:25 2012 +0200
@@ -196,8 +196,8 @@
 
         try:
             value, end = scan_once(s, end)
-        except StopIteration:
-            raise ValueError(errmsg("Expecting object", s, end))
+        except StopIteration as err:
+            raise ValueError(errmsg("Expecting value", s, err.value)) from None
         pairs_append((key, value))
         try:
             nextchar = s[end]
@@ -240,8 +240,8 @@
     while True:
         try:
             value, end = scan_once(s, end)
-        except StopIteration:
-            raise ValueError(errmsg("Expecting object", s, end))
+        except StopIteration as err:
+            raise ValueError(errmsg("Expecting value", s, err.value)) from None
         _append(value)
         nextchar = s[end:end + 1]
         if nextchar in _ws:
@@ -251,7 +251,7 @@
         if nextchar == ']':
             break
         elif nextchar != ',':
-            raise ValueError(errmsg("Expecting ',' delimiter", s, end))
+            raise ValueError(errmsg("Expecting ',' delimiter", s, end - 1))
         try:
             if s[end] in _ws:
                 end += 1
@@ -366,6 +366,6 @@
         """
         try:
             obj, end = self.scan_once(s, idx)
-        except StopIteration:
-            raise ValueError("No JSON object could be decoded")
+        except StopIteration as err:
+            raise ValueError(errmsg("Expecting value", s, err.value)) from None
         return obj, end
diff -r 1267d64c14b3 Lib/json/scanner.py
--- a/Lib/json/scanner.py	Thu Nov 01 14:52:03 2012 +0200
+++ b/Lib/json/scanner.py	Thu Nov 01 23:40:25 2012 +0200
@@ -29,7 +29,7 @@
         try:
             nextchar = string[idx]
         except IndexError:
-            raise StopIteration
+            raise StopIteration(idx)
 
         if nextchar == '"':
             return parse_string(string, idx + 1, strict)
@@ -60,7 +60,7 @@
         elif nextchar == '-' and string[idx:idx + 9] == '-Infinity':
             return parse_constant('-Infinity'), idx + 9
         else:
-            raise StopIteration
+            raise StopIteration(idx)
 
     def scan_once(string, idx):
         try:
diff -r 1267d64c14b3 Lib/test/json_tests/test_fail.py
--- a/Lib/test/json_tests/test_fail.py	Thu Nov 01 14:52:03 2012 +0200
+++ b/Lib/test/json_tests/test_fail.py	Thu Nov 01 23:40:25 2012 +0200
@@ -1,4 +1,5 @@
 from test.json_tests import PyTest, CTest
+import re
 
 # Fri Dec 30 18:57:26 2005
 JSONDOCS = [
@@ -82,6 +83,26 @@
         #This is for python encoder
         self.assertRaises(TypeError, self.dumps, data, indent=True)
 
+    def test_truncated_input(self):
+        test_cases = [
+            ('', 'Expecting value', 0),
+            ('[', 'Expecting value', 1),
+            ('[42', "Expecting ',' delimiter", 3),
+            ('[42,', 'Expecting value', 4),
+            ('{', 'Expecting property name enclosed in double quotes', 1),
+            ('{"', 'Unterminated string starting at', 1),
+            ('{"spam', 'Unterminated string starting at', 1),
+            ('{"spam"', "Expecting ':' delimiter", 7),
+            ('{"spam":', 'Expecting value', 8),
+            ('{"spam":42', "Expecting ',' delimiter", 10),
+            ('{"spam":42,', 'Expecting property name enclosed in double quotes', 11),
+        ]
+        for data, msg, idx in test_cases:
+            self.assertRaisesRegex(ValueError,
+                r'^{0}: line 1 column {1} \(char {1}\)'.format(
+                    re.escape(msg), idx),
+                self.loads, data)
+
 
 class TestPyFail(TestFail, PyTest): pass
 class TestCFail(TestFail, CTest): pass
diff -r 1267d64c14b3 Modules/_json.c
--- a/Modules/_json.c	Thu Nov 01 14:52:03 2012 +0200
+++ b/Modules/_json.c	Thu Nov 01 23:40:25 2012 +0200
@@ -272,6 +272,16 @@
     }
 }
 
+static void
+raise_stop_iteration(Py_ssize_t idx)
+{
+    PyObject *value = PyLong_FromSsize_t(idx);
+    if (value != NULL) {
+        PyErr_SetObject(PyExc_StopIteration, value);
+        Py_DECREF(value);
+    }
+}
+
 static PyObject *
 _build_rval_index_tuple(PyObject *rval, Py_ssize_t idx) {
     /* return (rval, idx) tuple, stealing reference to rval */
@@ -341,7 +351,7 @@
     buf = PyUnicode_DATA(pystr);
     kind = PyUnicode_KIND(pystr);
 
-    if (end < 0 || len <= end) {
+    if (end < 0 || len < end) {
         PyErr_SetString(PyExc_ValueError, "end is out of bounds");
         goto bail;
     }
@@ -639,12 +649,12 @@
     while (idx <= end_idx && IS_WHITESPACE(PyUnicode_READ(kind,str, idx))) idx++;
 
     /* only loop if the object is non-empty */
-    if (idx <= end_idx && PyUnicode_READ(kind, str, idx) != '}') {
-        while (idx <= end_idx) {
+    if (idx > end_idx || PyUnicode_READ(kind, str, idx) != '}') {
+        while (1) {
             PyObject *memokey;
 
             /* read key */
-            if (PyUnicode_READ(kind, str, idx) != '"') {
+            if (idx > end_idx || PyUnicode_READ(kind, str, idx) != '"') {
                 raise_errmsg("Expecting property name enclosed in double quotes", pystr, idx);
                 goto bail;
             }
@@ -701,11 +711,9 @@
             while (idx <= end_idx && IS_WHITESPACE(PyUnicode_READ(kind, str, idx))) idx++;
 
             /* bail if the object is closed or we didn't get the , delimiter */
-            if (idx > end_idx) break;
-            if (PyUnicode_READ(kind, str, idx) == '}') {
+            if (idx <= end_idx && PyUnicode_READ(kind, str, idx) == '}')
                 break;
-            }
-            else if (PyUnicode_READ(kind, str, idx) != ',') {
+            if (idx > end_idx || PyUnicode_READ(kind, str, idx) != ',') {
                 raise_errmsg("Expecting ',' delimiter", pystr, idx);
                 goto bail;
             }
@@ -716,12 +724,6 @@
         }
     }
 
-    /* verify that idx < end_idx, str[idx] should be '}' */
-    if (idx > end_idx || PyUnicode_READ(kind, str, idx) != '}') {
-        raise_errmsg("Expecting object", pystr, end_idx);
-        goto bail;
-    }
-
     *next_idx_ptr = idx + 1;
 
     if (has_pairs_hook) {
@@ -773,8 +775,8 @@
     while (idx <= end_idx && IS_WHITESPACE(PyUnicode_READ(kind, str, idx))) idx++;
 
     /* only loop if the array is non-empty */
-    if (idx <= end_idx && PyUnicode_READ(kind, str, idx) != ']') {
-        while (idx <= end_idx) {
+    if (idx > end_idx || PyUnicode_READ(kind, str, idx) != ']') {
+        while (1) {
 
             /* read any JSON term  */
             val = scan_once_unicode(s, pystr, idx, &next_idx);
@@ -791,11 +793,9 @@
             while (idx <= end_idx && IS_WHITESPACE(PyUnicode_READ(kind, str, idx))) idx++;
 
             /* bail if the array is closed or we didn't get the , delimiter */
-            if (idx > end_idx) break;
-            if (PyUnicode_READ(kind, str, idx) == ']') {
+            if (idx <= end_idx && PyUnicode_READ(kind, str, idx) == ']')
                 break;
-            }
-            else if (PyUnicode_READ(kind, str, idx) != ',') {
+            if (idx > end_idx || PyUnicode_READ(kind, str, idx) != ',') {
                 raise_errmsg("Expecting ',' delimiter", pystr, idx);
                 goto bail;
             }
@@ -808,7 +808,7 @@
 
     /* verify that idx < end_idx, PyUnicode_READ(kind, str, idx) should be ']' */
     if (idx > end_idx || PyUnicode_READ(kind, str, idx) != ']') {
-        raise_errmsg("Expecting object", pystr, end_idx);
+        raise_errmsg("Expecting value", pystr, end_idx);
         goto bail;
     }
     *next_idx_ptr = idx + 1;
@@ -876,7 +876,7 @@
     if (PyUnicode_READ(kind, str, idx) == '-') {
         idx++;
         if (idx > end_idx) {
-            PyErr_SetNone(PyExc_StopIteration);
+            raise_stop_iteration(start);
             return NULL;
         }
     }
@@ -892,7 +892,7 @@
     }
     /* no integer digits, error */
     else {
-        PyErr_SetNone(PyExc_StopIteration);
+        raise_stop_iteration(start);
         return NULL;
     }
 
@@ -985,7 +985,7 @@
     length = PyUnicode_GET_LENGTH(pystr);
 
     if (idx >= length) {
-        PyErr_SetNone(PyExc_StopIteration);
+        raise_stop_iteration(idx);
         return NULL;
     }