diff --git a/src/xmlsec/crypto.py b/src/xmlsec/crypto.py
index ff7f4335..97d4c879 100644
--- a/src/xmlsec/crypto.py
+++ b/src/xmlsec/crypto.py
@@ -124,8 +124,9 @@ def __init__(self, keyspec):
 
         self._private_callable, data = pk11.signer(keyspec)
         logging.debug("Using pkcs11 signing key: {!s}".format(self._private_callable))
-        cert = rsa_x509_pem.parse(data)
-        self.cert_pem = cert.get('pem')
+        if data is not None:
+            cert = rsa_x509_pem.parse(data)
+            self.cert_pem = cert.get('pem')
 
         self._from_keyspec = keyspec  # for debugging