diff --git a/src/_zkapauthorizer/_storage_client.py b/src/_zkapauthorizer/_storage_client.py
index 2c5a7af7393eb6677b86e99222f5d5131d3e94f8..0f7238ce8b8283a3e4f96075fcd13086dcd802fc 100644
--- a/src/_zkapauthorizer/_storage_client.py
+++ b/src/_zkapauthorizer/_storage_client.py
@@ -149,6 +149,19 @@ def with_rref(f):
     return g
 
 
+def _get_encoded_passes(passes):
+    """
+    :param list[Pass] passes: A group of passes to encode.
+
+    :return list[bytes]: The encoded form of the passes in the given group.
+    """
+    return list(
+        t.pass_text.encode("ascii")
+        for t
+        in passes
+    )
+
+
 @implementer(IStorageServer)
 @attr.s
 class ZKAPAuthorizerStorageClient(object):
@@ -200,20 +213,6 @@ class ZKAPAuthorizerStorageClient(object):
             )
         return rref
 
-    def _get_encoded_passes(self, message, count):
-        """
-        :param unicode message: The message to which to bind the passes.
-
-        :return: A list of passes from ``_get_passes`` encoded into their
-            ``bytes`` representation.
-        """
-        assert isinstance(message, unicode)
-        return list(
-            t.pass_text.encode("ascii")
-            for t
-            in self._get_passes(message.encode("utf-8"), count)
-        )
-
     @with_rref
     def get_version(self, rref):
         return rref.callRemote(
@@ -236,7 +235,7 @@ class ZKAPAuthorizerStorageClient(object):
         return call_with_passes(
             lambda passes: rref.callRemote(
                 "allocate_buckets",
-                passes,
+                _get_encoded_passes(passes),
                 storage_index,
                 renew_secret,
                 cancel_secret,
@@ -245,7 +244,7 @@ class ZKAPAuthorizerStorageClient(object):
                 canary,
             ),
             num_passes,
-            partial(self._get_encoded_passes, message),
+            partial(self._get_passes, message.encode("utf-8")),
         )
 
     @with_rref
@@ -278,13 +277,13 @@ class ZKAPAuthorizerStorageClient(object):
         result = yield call_with_passes(
             lambda passes: rref.callRemote(
                 "add_lease",
-                passes,
+                _get_encoded_passes(passes),
                 storage_index,
                 renew_secret,
                 cancel_secret,
             ),
             num_passes,
-            partial(self._get_encoded_passes, add_lease_message(storage_index)),
+            partial(self._get_passes, add_lease_message(storage_index).encode("utf-8")),
         )
         returnValue(result)
 
@@ -306,12 +305,12 @@ class ZKAPAuthorizerStorageClient(object):
         result = yield call_with_passes(
             lambda passes: rref.callRemote(
                 "renew_lease",
-                passes,
+                _get_encoded_passes(passes),
                 storage_index,
                 renew_secret,
             ),
             num_passes,
-            partial(self._get_encoded_passes, renew_lease_message(storage_index)),
+            partial(self._get_passes, renew_lease_message(storage_index).encode("utf-8")),
         )
         returnValue(result)
 
@@ -377,7 +376,7 @@ class ZKAPAuthorizerStorageClient(object):
         result = yield call_with_passes(
             lambda passes: rref.callRemote(
                 "slot_testv_and_readv_and_writev",
-                passes,
+                _get_encoded_passes(passes),
                 storage_index,
                 secrets,
                 tw_vectors,
@@ -385,8 +384,8 @@ class ZKAPAuthorizerStorageClient(object):
             ),
             num_passes,
             partial(
-                self._get_encoded_passes,
-                slot_testv_and_readv_and_writev_message(storage_index),
+                self._get_passes,
+                slot_testv_and_readv_and_writev_message(storage_index).encode("utf-8"),
             ),
         )
         returnValue(result)
diff --git a/src/_zkapauthorizer/tests/test_storage_protocol.py b/src/_zkapauthorizer/tests/test_storage_protocol.py
index bbe9abd749947e2bbd41e79a5696daec7e5e6998..1c84915add4de1d37ba4de7eab01c339352cbb3d 100644
--- a/src/_zkapauthorizer/tests/test_storage_protocol.py
+++ b/src/_zkapauthorizer/tests/test_storage_protocol.py
@@ -122,6 +122,9 @@ from ..storage_common import (
     get_implied_data_length,
     required_passes,
 )
+from .._storage_client import (
+    _get_encoded_passes,
+)
 from ..foolscap import (
     ShareStat,
 )
@@ -891,9 +894,11 @@ class ShareTests(TestCase):
         d = self.local_remote_server.callRemote(
             "slot_testv_and_readv_and_writev",
             # passes
-            self.client._get_encoded_passes(
-                slot_testv_and_readv_and_writev_message(storage_index),
-                1,
+            _get_encoded_passes(
+                self.pass_factory.get(
+                    slot_testv_and_readv_and_writev_message(storage_index),
+                    1,
+                ),
             ),
             # storage_index
             storage_index,