diff --git a/Doc/library/asyncio-subprocess.rst b/Doc/library/asyncio-subprocess.rst
index b6532618266..4713106eb5d 100644
--- a/Doc/library/asyncio-subprocess.rst
+++ b/Doc/library/asyncio-subprocess.rst
@@ -69,6 +69,9 @@ Run subprocesses asynchronously using the :mod:`subprocess` module.
    however, where :class:`~subprocess.Popen` takes a single argument which is
    list of strings, :func:`subprocess_exec` takes multiple string arguments.
 
+   The *protocol_factory* must instanciate a subclass of the
+   :class:`asyncio.SubprocessProtocol` class.
+
    Other parameters:
 
    * *stdin*: Either a file-like object representing the pipe to be connected
@@ -109,6 +112,9 @@ Run subprocesses asynchronously using the :mod:`subprocess` module.
    using the platform's "shell" syntax. This is similar to the standard library
    :class:`subprocess.Popen` class called with ``shell=True``.
 
+   The *protocol_factory* must instanciate a subclass of the
+   :class:`asyncio.SubprocessProtocol` class.
+
    See :meth:`~BaseEventLoop.subprocess_exec` for more details about
    the remaining arguments.