diff --git a/doc/src/connection.rst b/doc/src/connection.rst
index 2d483920..c6492632 100644
--- a/doc/src/connection.rst
+++ b/doc/src/connection.rst
@@ -348,7 +348,7 @@ The ``connection`` class
         pair: Transaction; Autocommit
         pair: Transaction; Isolation level
 
-    .. method:: set_session([isolation_level,] [readonly,] [deferrable,] [autocommit])
+    .. method:: set_session(isolation_level=None, readonly=None, deferrable=None, autocommit=None)
 
         Set one or more parameters for the next transactions or statements in
         the current session. See |SET TRANSACTION|_ for further details.
@@ -370,6 +370,7 @@ The ``connection`` class
             PostgreSQL session setting but an alias for setting the
             `autocommit` attribute.
 
+        Parameter passed as `!None` (the default for all) will not be changed.
         The parameters *isolation_level*, *readonly* and *deferrable* also
         accept the string ``DEFAULT`` as a value: the effect is to reset the
         parameter to the server default.