diff --git a/docs/fernet.rst b/docs/fernet.rst
index 02b9970..e4756c0 100644
--- a/docs/fernet.rst
+++ b/docs/fernet.rst
@@ -5,12 +5,13 @@
 
 .. testsetup::
 
+    import base64
     import binascii
-    key = binascii.unhexlify(b"0" * 64)
+    key = base64.urlsafe_b64encode(binascii.unhexlify(b"0" * 64))
 
 
 `Fernet`_ is an implementation of symmetric (also known as "secret key")
-authenticated cryptography. Fernet provides guarntees that a message encrypted
+authenticated cryptography. Fernet provides guarantees that a message encrypted
 using it cannot be manipulated or read without the key.
 
 .. class:: Fernet(key)
@@ -27,8 +28,9 @@
         >>> f.decrypt(ciphertext)
         'my deep dark secret'
 
-    :param bytes key: A 32-byte key. This **must** be kept secret. Anyone with
-                      this key is able to create and read messages.
+    :param bytes key: A base64 encoded 32-byte key. This **must** be kept
+                      secret. Anyone with this key is able to create and read
+                      messages.
 
 
     .. method:: encrypt(plaintext)