diff --git a/acme/acme/crypto_util.py b/acme/acme/crypto_util.py
index 84b70e4a6..de15284c0 100644
--- a/acme/acme/crypto_util.py
+++ b/acme/acme/crypto_util.py
@@ -218,7 +218,7 @@ def _pyopenssl_cert_or_req_san(cert_or_req):
     text = func(OpenSSL.crypto.FILETYPE_TEXT, cert_or_req).decode("utf-8")
     # WARNING: this function does not support multiple SANs extensions.
     # Multiple X509v3 extensions of the same type is disallowed by RFC 5280.
-    match = re.search(r"X509v3 Subject Alternative Name:\s*(.*)", text)
+    match = re.search(r"X509v3 Subject Alternative Name:(?: critical)?\s*(.*)", text)
     # WARNING: this function assumes that no SAN can include
     # parts_separator, hence the split!
     sans_parts = [] if match is None else match.group(1).split(parts_separator)
diff --git a/acme/acme/crypto_util_test.py b/acme/acme/crypto_util_test.py
index 845f43914..4046aa197 100644
--- a/acme/acme/crypto_util_test.py
+++ b/acme/acme/crypto_util_test.py
@@ -131,6 +131,11 @@ class PyOpenSSLCertOrReqSANTest(unittest.TestCase):
         self.assertEqual(self._call_csr('csr-idnsans.pem'),
                          self._get_idn_names())
 
+    def test_critical_san(self):
+        self.assertEqual(self._call_cert('critical-san.pem'),
+                         ['chicago-cubs.venafi.example', 'cubs.venafi.example'])
+
+
 
 class RandomSnTest(unittest.TestCase):
     """Test for random certificate serial numbers."""
diff --git a/acme/acme/testdata/critical-san.pem b/acme/acme/testdata/critical-san.pem
new file mode 100644
index 000000000..7aec8ab1c
--- /dev/null
+++ b/acme/acme/testdata/critical-san.pem
@@ -0,0 +1,28 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----
\ No newline at end of file