diff --git a/source/app/controllers/pacs/cfdi_cert.py b/source/app/controllers/pacs/cfdi_cert.py
index 2a0a7fe..d8ca7fc 100644
--- a/source/app/controllers/pacs/cfdi_cert.py
+++ b/source/app/controllers/pacs/cfdi_cert.py
@@ -224,7 +224,7 @@ class SATCertificate(object):
         args = f'openssl rsa -inform PEM -outform PEM -in "{str(path)}" -passin pass:{token}'
         pem = subprocess.check_output(args, shell=True).decode()
         key = serialization.load_pem_private_key(
-            pem.encode(), password=None, default_backend())
+            pem.encode(), password=None, backend=default_backend())
 
         digest = hashes.Hash(hashes.SHA512(), default_backend())
         digest.update(obj.rfc.encode())