diff --git a/docs/topics/auth/default.txt b/docs/topics/auth/default.txt
index e666cded75..8849520b11 100644
--- a/docs/topics/auth/default.txt
+++ b/docs/topics/auth/default.txt
@@ -939,10 +939,15 @@ provides several built-in forms located in :mod:`django.contrib.auth.forms`:
 
     A form used in the admin interface to change a user's password.
 
+    Takes the ``user`` as the first positional argument.
+
 .. class:: AuthenticationForm
 
     A form for logging a user in.
 
+    Takes ``request`` as its first positional argument, which is stored on the
+    form instance for use by sub-classes.
+
 .. class:: PasswordChangeForm
 
     A form for allowing a user to change their password.