Consistent a/an for x509.
diff --git a/OpenSSL/crypto.py b/OpenSSL/crypto.py
index 0272dd6..28a1589 100644
--- a/OpenSSL/crypto.py
+++ b/OpenSSL/crypto.py
@@ -1392,12 +1392,12 @@
"""
An X.509 store context.
- A :py:class:`X509StoreContext` is used to verify a certificate in some
+ An :py:class:`X509StoreContext` is used to verify a certificate in some
context in conjunction with :py:func:`verify_cert`. The information
encapsulated in this object includes, but is not limited to, a set of
trusted certificates, verification parameters and revoked certificates.
- :param store: A :py:class:`X509Store` of trusted certificates.
+ :param store: An :py:class:`X509Store` of trusted certificates.
:param cert: An :py:class:`X509` certificate to be validated during a
subsequent call to :py:func:`verify_cert`.
"""