CRLNumber needs to be a class for reasons.
diff --git a/docs/x509/reference.rst b/docs/x509/reference.rst
index dace8c1..f53eae0 100644
--- a/docs/x509/reference.rst
+++ b/docs/x509/reference.rst
@@ -1695,6 +1695,27 @@
:type: int
+.. class:: CRLNumber(crl_number)
+
+ .. versionadded:: 1.2
+
+ The CRL number is a non-critical CRL extension that conveys a
+ monotonically increasing sequence number for a given CRL scope and
+ CRL issuer. This extension allows users to easily determine when a
+ particular CRL supersedes another CRL. :rfc:`5280` requires that this
+ extension be present in conforming CRLs.
+
+ .. attribute:: oid
+
+ :type: :class:`ObjectIdentifier`
+
+ Returns
+ :attr:`~cryptography.x509.oid.ExtensionOID.CRL_NUMBER`.
+
+ .. attribute:: crl_number
+
+ :type: int
+
.. class:: CertificatePolicies(policies)
.. versionadded:: 0.9