diff --git a/docs/x509/reference.rst b/docs/x509/reference.rst
index 14fc37c..3051308 100644
--- a/docs/x509/reference.rst
+++ b/docs/x509/reference.rst
@@ -1871,6 +1871,12 @@
     identifier. For more information about the use of this extension see
     :rfc:`5280`.
 
+    .. attribute:: oid
+
+        :type: :class:`ObjectIdentifier`
+
+        Returns :attr:`~cryptography.x509.oid.ExtensionOID.POLICY_CONSTRAINTS`.
+
     .. attribute:: require_explicit_policy
 
         :type: int or None
diff --git a/src/cryptography/x509/extensions.py b/src/cryptography/x509/extensions.py
index ba9cb37..0aa6721 100644
--- a/src/cryptography/x509/extensions.py
+++ b/src/cryptography/x509/extensions.py
@@ -491,6 +491,8 @@
 
 @utils.register_interface(ExtensionType)
 class PolicyConstraints(object):
+    oid = ExtensionOID.POLICY_CONSTRAINTS
+
     def __init__(self, require_explicit_policy, inhibit_policy_mapping):
         if require_explicit_policy is not None and not isinstance(
             require_explicit_policy, six.integer_types