diff --git a/Doc/library/multiprocessing.rst b/Doc/library/multiprocessing.rst
index 0007591..7225b65 100644
--- a/Doc/library/multiprocessing.rst
+++ b/Doc/library/multiprocessing.rst
@@ -951,7 +951,8 @@
    use.  The number of usable CPUs can be obtained with
    ``len(os.sched_getaffinity(0))``
 
-   May raise :exc:`NotImplementedError`.
+   When the number of CPUs cannot be determined a :exc:`NotImplementedError`
+   is raised.
 
    .. seealso::
       :func:`os.cpu_count`