diff -r 8b0c2c7cb4a7 Objects/longobject.c
--- a/Objects/longobject.c	Fri Sep 18 15:38:37 2015 +0200
+++ b/Objects/longobject.c	Fri Sep 18 15:47:12 2015 +0200
@@ -4495,11 +4495,13 @@ PyObject *
 simple:
     assert(Py_REFCNT(a) > 0);
     assert(Py_REFCNT(b) > 0);
-#if LONG_MAX >> 2*PyLong_SHIFT
+/* Issue #24999: use two shifts instead of ">> 2*PyLong_SHIFT" to avoid
+   undefined behaviour when LONG_MAX type is smaller than 60 bits */
+#if LONG_MAX >> PyLong_SHIFT >> PyLong_SHIFT
     /* a fits into a long, so b must too */
     x = PyLong_AsLong((PyObject *)a);
     y = PyLong_AsLong((PyObject *)b);
-#elif defined(PY_LONG_LONG) && PY_LLONG_MAX >> 2*PyLong_SHIFT
+#elif defined(PY_LONG_LONG) && PY_LLONG_MAX >> PyLong_SHIFT >> PyLong_SHIFT
     x = PyLong_AsLongLong((PyObject *)a);
     y = PyLong_AsLongLong((PyObject *)b);
 #else