diff --git a/pypy/module/cpyext/intobject.py b/pypy/module/cpyext/intobject.py
--- a/pypy/module/cpyext/intobject.py
+++ b/pypy/module/cpyext/intobject.py
@@ -6,7 +6,7 @@
     PyObject, PyObjectFields, CONST_STRING, CANNOT_FAIL, Py_ssize_t)
 from pypy.module.cpyext.pyobject import (
     make_typedescr, track_reference, RefcountState, from_ref)
-from pypy.rlib.rarithmetic import r_uint, intmask, LONG_TEST
+from pypy.rlib.rarithmetic import r_uint, intmask, LONG_TEST, r_ulonglong
 from pypy.objspace.std.intobject import W_IntObject
 import sys
 
@@ -83,6 +83,20 @@
         num = space.bigint_w(w_int)
         return num.uintmask()
 
+@cpython_api([PyObject], rffi.ULONGLONG, error=-1)
+def PyInt_AsUnsignedLongLongMask(space, w_obj):
+    """Will first attempt to cast the object to a PyIntObject or
+    PyLongObject, if it is not already one, and then return its value as
+    unsigned long long, without checking for overflow.
+    """
+    w_int = space.int(w_obj)
+    if space.is_true(space.isinstance(w_int, space.w_int)):
+        num = space.int_w(w_int)
+        return r_ulonglong(num)
+    else:
+        num = space.bigint_w(w_int)
+        return num.ulonglongmask()
+
 @cpython_api([PyObject], lltype.Signed, error=CANNOT_FAIL)
 def PyInt_AS_LONG(space, w_int):
     """Return the value of the object w_int. No error checking is performed."""
diff --git a/pypy/module/cpyext/test/test_intobject.py b/pypy/module/cpyext/test/test_intobject.py
--- a/pypy/module/cpyext/test/test_intobject.py
+++ b/pypy/module/cpyext/test/test_intobject.py
@@ -34,6 +34,11 @@
         assert (api.PyInt_AsUnsignedLongMask(space.wrap(10**30))
                 == 10**30 % ((sys.maxint + 1) * 2))
 
+        assert (api.PyInt_AsUnsignedLongLongMask(space.wrap(sys.maxint))
+                == sys.maxint)
+        assert (api.PyInt_AsUnsignedLongLongMask(space.wrap(10**30))
+                == 10**30 % (2**64))
+
     def test_coerce(self, space, api):
         class Coerce(object):
             def __int__(self):