diff --git a/src/cryptography/hazmat/backends/openssl/x509.py b/src/cryptography/hazmat/backends/openssl/x509.py
index 63e4a17..1c0c3ac 100644
--- a/src/cryptography/hazmat/backends/openssl/x509.py
+++ b/src/cryptography/hazmat/backends/openssl/x509.py
@@ -235,7 +235,12 @@
                     )
             else:
                 d2i = backend._lib.X509V3_EXT_d2i(ext)
-                assert d2i != backend._ffi.NULL
+                if d2i == backend._ffi.NULL:
+                    backend._consume_errors()
+                    raise ValueError(
+                        "The {0} extension appears to be corrupt".format(oid)
+                    )
+
                 value = handler(backend, d2i)
                 extensions.append(x509.Extension(oid, critical, value))
 
diff --git a/tests/test_x509_ext.py b/tests/test_x509_ext.py
index 7b13582..2980808 100644
--- a/tests/test_x509_ext.py
+++ b/tests/test_x509_ext.py
@@ -2853,3 +2853,18 @@
             x509.OID_INHIBIT_ANY_POLICY
         ).value
         assert iap.skip_certs == 5
+
+
+@pytest.mark.requires_backend_interface(interface=RSABackend)
+@pytest.mark.requires_backend_interface(interface=X509Backend)
+class TestCorruptExtension(object):
+    def test_invalid_certificate_policies_data(self, backend):
+        cert = _load_cert(
+            os.path.join(
+                "x509", "custom", "cp_invalid.pem"
+            ),
+            x509.load_pem_x509_certificate,
+            backend
+        )
+        with pytest.raises(ValueError):
+            cert.extensions