diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst
--- a/Doc/library/stdtypes.rst
+++ b/Doc/library/stdtypes.rst
@@ -955,7 +955,8 @@
    items with index  ``x = i + n*k`` such that ``0 <= n < (j-i)/k``.  In other words,
    the indices are ``i``, ``i+k``, ``i+2*k``, ``i+3*k`` and so on, stopping when
    *j* is reached (but never including *j*).  If *i* or *j* is greater than
-   ``len(s)``, use ``len(s)``.  If *i* or *j* are omitted or ``None``, they become
+   ``len(s)``, use ``len(s)`` if *k* is positive, or ``len(s) - 1`` if *k* is
+   negative.  If *i* or *j* are omitted or ``None``, they become
    "end" values (which end depends on the sign of *k*).  Note, *k* cannot be zero.
    If *k* is ``None``, it is treated like ``1``.