diff --git a/scripts/audit-validity-dates.py b/scripts/audit-validity-dates.py
index 123f7bdc0..660a53b91 100755
--- a/scripts/audit-validity-dates.py
+++ b/scripts/audit-validity-dates.py
@@ -105,8 +105,10 @@ class AuditData:
         # CertificateRevocationList expires after "next_update"
         # CertificateRevocationList is invalid before "last_update"
         elif self.data_type == DataType.CRL:
-            self.not_valid_after = x509_obj.next_update
             assert isinstance(x509_obj, cryptography.x509.CertificateRevocationList)
+            self.not_valid_after = \
+                datetime.datetime.max if x509_obj.next_update is None else \
+                x509_obj.next_update
             self.not_valid_before = x509_obj.last_update
         # CertificateSigningRequest is always valid.
         elif self.data_type == DataType.CSR: