diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst
index e3bd1a46891adc..b0388c4e1f0bd4 100644
--- a/Doc/library/stdtypes.rst
+++ b/Doc/library/stdtypes.rst
@@ -2747,6 +2747,8 @@ expression support in the :mod:`re` module).
    The *chars* argument is not a prefix or suffix; rather, all combinations of its
    values are stripped.
 
+   Whitespace characters are defined by :meth:`str.isspace`.
+
    For example:
 
    .. doctest::