diff -urp Python-2.7.5.orig/Python/bltinmodule.c Python-2.7.5/Python/bltinmodule.c
--- Python-2.7.5.orig/Python/bltinmodule.c	2013-05-12 06:32:53.000000000 +0300
+++ Python-2.7.5/Python/bltinmodule.c	2013-07-04 10:38:53.000000000 +0300
@@ -2313,13 +2313,6 @@ builtin_sum(PyObject *self, PyObject *ar
             return NULL;
         }
     } else {
-        /* reject string values for 'start' parameter */
-        if (PyObject_TypeCheck(result, &PyBaseString_Type)) {
-            PyErr_SetString(PyExc_TypeError,
-                "sum() can't sum strings [use ''.join(seq) instead]");
-            Py_DECREF(iter);
-            return NULL;
-        }
         Py_INCREF(result);
     }
 
@@ -2399,6 +2392,97 @@ builtin_sum(PyObject *self, PyObject *ar
             }
         }
     }
+
+    long subclass_flags = 0;
+    if (PyList_CheckExact(result))
+        subclass_flags = Py_TPFLAGS_LIST_SUBCLASS;
+    else if (PyTuple_CheckExact(result))
+        subclass_flags = Py_TPFLAGS_TUPLE_SUBCLASS;
+    else if (PyString_CheckExact(result))
+        subclass_flags = Py_TPFLAGS_STRING_SUBCLASS;
+
+    if (subclass_flags) {
+        PyObject *l_result = PyList_New(0);
+        if (l_result == NULL) {
+            Py_DECREF(result);
+            Py_DECREF(iter);
+            return NULL;
+        }
+        temp = _PyList_Extend((PyListObject*)l_result, result);
+        Py_DECREF(result);
+        result = NULL;
+        if (temp == NULL) {
+            Py_DECREF(l_result);
+            Py_DECREF(iter);
+            return NULL;
+        }
+        Py_DECREF(temp);
+        for (;;) {
+            item = PyIter_Next(iter);
+            if (item == NULL) {
+                if (PyErr_Occurred()) {
+                    Py_DECREF(l_result);
+                    return NULL;
+                }
+                break;
+            }
+            if (!PyType_FastSubclass(Py_TYPE(item), subclass_flags))
+                break;
+            temp = _PyList_Extend((PyListObject*)l_result, item);
+            if (temp == NULL)
+                break;
+            Py_DECREF(item);
+            Py_DECREF(temp);
+        }
+        /* Not a subclass, could not extend, or end of sequence. Restore real objects ... */
+        if (subclass_flags == Py_TPFLAGS_LIST_SUBCLASS)
+            result = l_result;
+        else if (subclass_flags == Py_TPFLAGS_TUPLE_SUBCLASS) {
+            result = PyList_AsTuple(l_result);
+            Py_DECREF(l_result);
+            if (result == NULL) {
+                Py_DECREF(item);
+                Py_DECREF(iter);
+                return NULL;
+            }
+        }
+        else /* subclass_flags == Py_TPFLAGS_STRING_SUBCLASS */ {
+            char *p;
+            Py_ssize_t i;
+            PyObject *char_string;
+            size_t sz = PyList_GET_SIZE(l_result);
+            /* Allocate result space. */
+            result = PyString_FromStringAndSize((char*)NULL, sz);
+            if (result == NULL) {
+                Py_DECREF(l_result);
+                Py_DECREF(item);
+                Py_DECREF(iter);
+                return NULL;
+            }
+            /* Catenate everything. */
+            p = PyString_AS_STRING(result);
+            for (i = 0; i < sz; ++i) {
+                char_string = PyList_GET_ITEM(l_result, i);
+                *p++ = *PyString_AS_STRING(char_string);
+            }
+            Py_DECREF(l_result);
+        }
+        /* ... and process normally */
+        if (item == NULL) {
+            Py_DECREF(iter);
+            return result;
+        }
+        else {
+            temp = PyNumber_Add(result, item);
+            Py_DECREF(result);
+            Py_DECREF(item);
+            result = temp;
+            if (result == NULL) {
+                Py_DECREF(iter);
+                return NULL;
+            }
+        }
+    }
 #endif
 
     for(;;) {