diff --git a/Doc/library/asyncio-eventloop.rst b/Doc/library/asyncio-eventloop.rst
index 586623b5a78bb3..8027d3525e5999 100644
--- a/Doc/library/asyncio-eventloop.rst
+++ b/Doc/library/asyncio-eventloop.rst
@@ -960,6 +960,9 @@ Watching file descriptors
    invoke *callback* with the specified arguments once *fd* is available for
    reading.
 
+   Any preexisting callback registered for *fd* is cancelled and replaced by
+   *callback*.
+
 .. method:: loop.remove_reader(fd)
 
    Stop monitoring the *fd* file descriptor for read availability. Returns
@@ -971,6 +974,9 @@ Watching file descriptors
    invoke *callback* with the specified arguments once *fd* is available for
    writing.
 
+   Any preexisting callback registered for *fd* is cancelled and replaced by
+   *callback*.
+
    Use :func:`functools.partial` :ref:`to pass keyword arguments
    <asyncio-pass-keywords>` to *callback*.