diff --git a/src/cryptography/hazmat/backends/openssl/backend.py b/src/cryptography/hazmat/backends/openssl/backend.py
index 0e0ca53a79241..0d35fae0c1b44 100644
--- a/src/cryptography/hazmat/backends/openssl/backend.py
+++ b/src/cryptography/hazmat/backends/openssl/backend.py
@@ -1188,7 +1188,33 @@ def _create_x509_extension(self, handlers, rust_handler, extension):
         )
 
     def _convert_x509_extension_to_bytes(self, extension):
-        ext = self._create_x509_extension(self._all_encode_handlers, extension)
+        if isinstance(extension.value, x509.UnrecognizedExtension):
+            return extension.value.value
+
+        for rust_handler in [
+            rust_x509.encode_certificate_extension,
+            rust_x509.encode_crl_extension,
+            rust_x509.encode_crl_entry_extension,
+            rust_ocsp.encode_ocsp_request_extension,
+            rust_ocsp.encode_ocsp_basic_response_extension,
+        ]:
+            try:
+                return rust_handler(extension)
+            except NotImplementedError:
+                pass
+
+        # Once all extensions are handled by Rust code, the following needs to
+        # be replaced by something like:
+        #     raise NotImplementedError(
+        #         f"Extension not supported: {extension.oid.dotted_string}"
+        #     )
+
+        ext = self._create_x509_extension(
+            self._all_encode_handlers,
+            # pick a random one here:
+            rust_handler=rust_x509.encode_certificate_extension,
+            extension=extension,
+        )
         data = self._lib.X509_EXTENSION_get_data(ext)
         self.openssl_assert(data != self._ffi.NULL)
         return self._ffi.buffer(data.data, data.length)[:]
diff --git a/tests/x509/test_x509_ext.py b/tests/x509/test_x509_ext.py
index 3a8d78168df77..25721089344a2 100644
--- a/tests/x509/test_x509_ext.py
+++ b/tests/x509/test_x509_ext.py
@@ -198,6 +198,12 @@ def test_indexing(self):
         assert ext[-1] == ext[1]
         assert ext[0] == x509.TLSFeatureType.status_request
 
+    def test_der_string(self):
+        ext1 = x509.TLSFeature([x509.TLSFeatureType.status_request])
+        assert ext1.to_der_string() == b"\x30\x03\x02\x01\x05"
+        ext2 = x509.TLSFeature([x509.TLSFeatureType.status_request_v2])
+        assert ext2.to_der_string() == b"\x30\x03\x02\x01\x11"
+
 
 class TestUnrecognizedExtension(object):
     def test_invalid_oid(self):
@@ -251,6 +257,20 @@ def test_hash(self):
         assert hash(ext1) == hash(ext2)
         assert hash(ext1) != hash(ext3)
 
+    def test_der_string(self):
+        ext1 = x509.UnrecognizedExtension(
+            x509.ObjectIdentifier("1.2.3.5"), b"\x03\x02\x01"
+        )
+        assert ext1.to_der_string() == b"\x03\x02\x01"
+
+        # The following creates a BasicConstraints extension with an invalid
+        # value. The serialization code should still handle it correctly by
+        # special-casing UnrecognizedExtension.
+        ext2 = x509.UnrecognizedExtension(
+            x509.oid.ExtensionOID.BASIC_CONSTRAINTS, b"\x03\x02\x01"
+        )
+        assert ext2.to_der_string() == b"\x03\x02\x01"
+
 
 class TestCertificateIssuer(object):
     def test_iter_names(self):
@@ -2159,6 +2179,10 @@ def test_hash(self):
         assert hash(c1) == hash(c2)
         assert hash(c1) != hash(c3)
 
+    def test_der_string(self):
+        ext = x509.CRLNumber(15)
+        assert ext.to_der_string() == b"\x02\x01\x0f"
+
 
 class TestSubjectAlternativeName(object):
     def test_get_values_for_type(self):
@@ -2701,6 +2725,13 @@ def test_require_explicit_policy(self, backend):
             inhibit_policy_mapping=None,
         )
 
+    def test_der_string(self):
+        ext = x509.PolicyConstraints(
+            require_explicit_policy=None,
+            inhibit_policy_mapping=0,
+        )
+        assert ext.to_der_string() == b"\x30\x03\x81\x01\x00"
+
 
 class TestAuthorityInformationAccess(object):
     def test_invalid_descriptions(self):
@@ -5640,6 +5671,10 @@ def test_hash(self):
         assert hash(nonce1) == hash(nonce2)
         assert hash(nonce1) != hash(nonce3)
 
+    def test_der_string(self):
+        ext = x509.OCSPNonce(b"0" * 5)
+        assert ext.to_der_string() == b"00000"
+
 
 def test_all_extension_oid_members_have_names_defined():
     for oid in dir(ExtensionOID):