diff --git a/signxml/xades/xades.py b/signxml/xades/xades.py
index efa3ec1..6ffcb63 100644
--- a/signxml/xades/xades.py
+++ b/signxml/xades/xades.py
@@ -274,7 +274,7 @@ def _verify_signing_time(self, verify_result: VerifyResult):
 
     def _verify_cert_digest(self, signing_cert_node, expect_cert, idx):
         cert = self._find(signing_cert_node, "xades:Cert[{0}]".format(idx), False)
-        if cert != None:
+        if cert is not None:
             cert_digest = self._find(cert, "xades:CertDigest")
             digest_alg = DigestAlgorithm(self._find(cert_digest, "DigestMethod").get("Algorithm"))
             digest_value = self._find(cert_digest, "DigestValue")