diff --git a/src/allmydata/crypto/aes.py b/src/allmydata/crypto/aes.py
index dd496e6bd..a2ab36927 100644
--- a/src/allmydata/crypto/aes.py
+++ b/src/allmydata/crypto/aes.py
@@ -19,7 +19,7 @@ from cryptography.hazmat.primitives.ciphers import (
 )
 
 
-DEFAULT_IV = '\x00' * 16
+DEFAULT_IV = b'\x00' * 16
 
 
 def create_encryptor(key, iv=None):