diff --git a/Doc/library/logging.rst b/Doc/library/logging.rst
index 5795645f71d1cd..a5f34665d5cb2b 100644
--- a/Doc/library/logging.rst
+++ b/Doc/library/logging.rst
@@ -562,7 +562,8 @@ subclasses. However, the :meth:`!__init__` method in subclasses needs to call
 
    .. method:: Handler.setFormatter(fmt)
 
-      Sets the :class:`Formatter` for this handler to *fmt*.
+      Sets the formatter for this handler to *fmt*.
+      The *fmt* argument must be a :class:`Formatter` instance or ``None``.
 
 
    .. method:: Handler.addFilter(filter)