diff --git a/Doc/library/imaplib.rst b/Doc/library/imaplib.rst
index 8e77f7db925d98..dbee7a6be80081 100644
--- a/Doc/library/imaplib.rst
+++ b/Doc/library/imaplib.rst
@@ -635,3 +635,10 @@ retrieves and prints all messages::
    M.close()
    M.logout()
 
+.. note::
+
+   A ``FETCH`` response may contain additional or unsolicited data
+   (see :rfc:`3501`, section 7.4.2),
+   so production code should inspect the whole response
+   rather than rely on ``data[0][1]``.
+