diff --git a/requests_pkcs12.py b/requests_pkcs12.py
index 3d3522e..30bad9c 100644
--- a/requests_pkcs12.py
+++ b/requests_pkcs12.py
@@ -34,7 +34,7 @@
     from ssl import PROTOCOL_SSLv23 as default_ssl_protocol
 
 def _check_cert_not_after(cert):
-    cert_not_after = cert.not_valid_after
+    cert_not_after = cert.not_valid_after_utc
     if cert_not_after < datetime.datetime.utcnow():
         raise ValueError('Client certificate expired: Not After: {cert_not_after:%Y-%m-%d %H:%M:%SZ}'.format(**locals()))
 
diff --git a/setup.py b/setup.py
index 1c5a160..4a887e6 100644
--- a/setup.py
+++ b/setup.py
@@ -8,9 +8,9 @@
     author='Volker Diels-Grabsch',
     author_email='volker.diels-grabsch@m-click.aero',
     license='ISC',
-    python_requires='>=3.6',
+    python_requires='>=3.7',
     install_requires=[
-        'cryptography (>=3.4.7)',
+        'cryptography (>=42.0.0)',
         'requests (>=2.26.0)',
     ],
     extras_require={