Issue #21362: concurrent.futures does not validate that max_workers is proper
diff --git a/Doc/library/concurrent.futures.rst b/Doc/library/concurrent.futures.rst
index 0495737..08c926a 100644
--- a/Doc/library/concurrent.futures.rst
+++ b/Doc/library/concurrent.futures.rst
@@ -175,6 +175,8 @@
An :class:`Executor` subclass that executes calls asynchronously using a pool
of at most *max_workers* processes. If *max_workers* is ``None`` or not
given, it will default to the number of processors on the machine.
+ If *max_workers* is lower or equal to ``0``, then a :exc:`ValueError`
+ will be raised.
.. versionchanged:: 3.3
When one of the worker processes terminates abruptly, a