diff --git a/tests/hazmat/primitives/test_3des.py b/tests/hazmat/primitives/test_3des.py
index 586afb4..f281ba2 100644
--- a/tests/hazmat/primitives/test_3des.py
+++ b/tests/hazmat/primitives/test_3des.py
@@ -170,7 +170,7 @@
 
 @pytest.mark.supported(
     only_if=lambda backend: backend.cipher_supported(
-        algorithms.TripleDES("\x00" * 8), modes.ECB()
+        algorithms.TripleDES(b"\x00" * 8), modes.ECB()
     ),
     skip_message="Does not support TripleDES ECB",
 )