bytes
diff --git a/tests/test_crypto.py b/tests/test_crypto.py
index e90c868..a344f1c 100644
--- a/tests/test_crypto.py
+++ b/tests/test_crypto.py
@@ -3186,7 +3186,7 @@
         """
         crl = CRL()
         revoked = Revoked()
-        revoked.set_serial("01")
+        revoked.set_serial(b"01")
         revoked.set_rev_date(b"20160310020145Z")
         crl.add_revoked(revoked=revoked)
         self.assertTrue(isinstance(crl.get_revoked()[0], Revoked))