diff --git a/src/allmydata/crypto/aes.py b/src/allmydata/crypto/aes.py
index a2ab36927..e9d61df34 100644
--- a/src/allmydata/crypto/aes.py
+++ b/src/allmydata/crypto/aes.py
@@ -48,7 +48,7 @@ def encrypt_data(encryptor, plaintext):
 
     :param bytes plaintext: the data to encrypt
 
-    :returns: ciphertext
+    :returns: bytes of ciphertext
     """
 
     _validate_encryptor(encryptor)