diff --git a/src/cryptography/x509/extensions.py b/src/cryptography/x509/extensions.py
index 6ae0092..2363d2b 100644
--- a/src/cryptography/x509/extensions.py
+++ b/src/cryptography/x509/extensions.py
@@ -132,6 +132,9 @@
     def __ne__(self, other):
         return not self == other
 
+    def __hash__(self):
+        return hash(self.crl_number)
+
     def __repr__(self):
         return "<CRLNumber({0})>".format(self.crl_number)
 
diff --git a/tests/test_x509_ext.py b/tests/test_x509_ext.py
index b8105a4..49a3433 100644
--- a/tests/test_x509_ext.py
+++ b/tests/test_x509_ext.py
@@ -1579,6 +1579,13 @@
         with pytest.raises(TypeError):
             x509.CRLNumber("notanumber")
 
+    def test_hash(self):
+        c1 = x509.CRLNumber(1)
+        c2 = x509.CRLNumber(1)
+        c3 = x509.CRLNumber(2)
+        assert hash(c1) == hash(c2)
+        assert hash(c1) != hash(c3)
+
 
 class TestSubjectAlternativeName(object):
     def test_get_values_for_type(self):