diff -r 19488e23dcdb Objects/longobject.c
--- a/Objects/longobject.c	Fri Jun 03 10:48:43 2016 +0300
+++ b/Objects/longobject.c	Fri Jun 03 17:11:14 2016 +0300
@@ -71,7 +71,8 @@
 #endif
 
 /* If a freshly-allocated int is already shared, it must
-   be a small integer, so negating it must go to PyLong_FromLong */
+   be a small integer, so unless it is zero, negating it 
+   must go to PyLong_FromLong */
 Py_LOCAL_INLINE(void)
 _PyLong_Negate(PyLongObject **x_p)
 {
@@ -83,6 +84,9 @@
         return;
     }
 
+    if (Py_SIZE(x) == 0)
+        return;
+
     *x_p = (PyLongObject *)PyLong_FromLong(-MEDIUM_VALUE(x));
     Py_DECREF(x);
 }
@@ -2975,6 +2979,9 @@
             ;
         if (i < 0)
             return (PyLongObject *)PyLong_FromLong(0);
+        if (i == 0)
+            return (PyLongObject *)PyLong_FromLong((sdigit)a->ob_digit[0] - 
+                                                   (sdigit)b->ob_digit[0]);
         if (a->ob_digit[i] < b->ob_digit[i]) {
             sign = -1;
             { PyLongObject *temp = a; a = b; b = temp; }
@@ -3004,7 +3011,7 @@
         if (z == NULL)
             return NULL;
     }
-    return long_normalize(z);
+    return maybe_small_long(long_normalize(z));
 }
 
 static PyObject *
@@ -3055,7 +3062,9 @@
         else
             z = x_add(a, b);
         if (z != NULL && Py_SIZE(z) != 0)
-            Py_SIZE(z) = -(Py_SIZE(z));
+            _PyLong_Negate(&z);
+            if (z == NULL)
+                return NULL;
     }
     else {
         if (Py_SIZE(b) < 0)