diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
index 7bb5687..9085502 100644
--- a/Python/bltinmodule.c
+++ b/Python/bltinmodule.c
@@ -2366,8 +2366,15 @@ builtin_sum_impl(PyObject *module, PyObject *iterable, PyObject *start)
                 return PyLong_FromLong(i_result);
             }
             if (PyLong_CheckExact(item)) {
-                long b = PyLong_AsLongAndOverflow(item, &overflow);
-                long x = i_result + b;
+                long b, x;
+                overflow = 0;
+                switch (Py_SIZE(item)) {
+                    case -1: b = -(sdigit) ((PyLongObject*)item)->ob_digit[0]; break;
+                    case  0: continue;
+                    case  1: b = ((PyLongObject*)item)->ob_digit[0]; break;
+                    default: b = PyLong_AsLongAndOverflow(item, &overflow); break;
+                }
+                x = i_result + b;
                 if (overflow == 0 && ((x^i_result) >= 0 || (x^b) >= 0)) {
                     i_result = x;
                     Py_DECREF(item);