update doc language
diff --git a/docs/x509.rst b/docs/x509.rst
index 3cf4f90..f9992e2 100644
--- a/docs/x509.rst
+++ b/docs/x509.rst
@@ -816,15 +816,16 @@
:type: list of :class:`GeneralName` instances or None
- This field describes methods to retrieve the CRL. If this is not None
- then ``relative_name`` must be None.
+ This field describes methods to retrieve the CRL. At most one of
+ ``full_name`` or ``relative_name`` will be non-None.
.. attribute:: relative_name
:type: :class:`Name` or None
This field describes methods to retrieve the CRL relative to the CRL
- issuer. If this is not None then ``full_name`` must be None.
+ issuer. At most one of ``full_name`` or ``relative_name`` will be
+ non-None.
.. attribute:: crl_issuer