diff --git a/doc/src/usage.rst b/doc/src/usage.rst
index 1da8572f..e43219d6 100644
--- a/doc/src/usage.rst
+++ b/doc/src/usage.rst
@@ -100,7 +100,8 @@ many placeholders can use the same values::
     ...     {'int': 10, 'str': "O'Reilly", 'date': datetime.date(2005, 11, 18)})
 
 When parameters are used, in order to include a literal ``%`` in the query you
-can use the ``%%`` string.
+can use the ``%%`` string. Using characters ``%``, ``(``, ``)`` in the
+argument names is not supported.
 
 While the mechanism resembles regular Python strings manipulation, there are a
 few subtle differences you should care about when passing parameters to a