diff --git a/docs/x509.rst b/docs/x509.rst
index 36e9fab..1321891 100644
--- a/docs/x509.rst
+++ b/docs/x509.rst
@@ -284,7 +284,7 @@
 
         :type: :class:`ObjectIdentifier`
 
-        The extension OID.
+        The :ref:`extension OID <extension_oids>`.
 
     .. attribute:: critical
 
@@ -485,6 +485,8 @@
     Corresponds to the dotted string ``2.16.840.1.101.3.4.3.2"``. This is
     a SHA256 digest signed by a DSA key.
 
+.. _extension_oids:
+
 Extension OIDs
 ~~~~~~~~~~~~~~
 
diff --git a/src/cryptography/x509.py b/src/cryptography/x509.py
index 43ece92..556e5a3 100644
--- a/src/cryptography/x509.py
+++ b/src/cryptography/x509.py
@@ -177,9 +177,8 @@
             raise ValueError("path_length must be None when ca is False")
 
         if (
-            path_length is not None and (not isinstance(
-                path_length, six.integer_types
-            ) or path_length < 0)
+            path_length is not None and
+            (not isinstance(path_length, six.integer_types) or path_length < 0)
         ):
             raise TypeError(
                 "path_length must be a non-negative integer or None"