diff --git a/src/_zkapauthorizer/_storage_client.py b/src/_zkapauthorizer/_storage_client.py
index 55ccdb0c5db4d30e6977a90fad7f1f4de08d7a22..b24085b4c0193e37f09f40030f1c9425ee44b261 100644
--- a/src/_zkapauthorizer/_storage_client.py
+++ b/src/_zkapauthorizer/_storage_client.py
@@ -70,7 +70,7 @@ class ZKAPAuthorizerStorageClient(object):
         return list(
             t.text.encode("ascii")
             for t
-            in self._get_passes(message, count)
+            in self._get_passes(message.encode("hex"), count)
         )
 
     def get_version(self):