diff --git a/src/allmydata/storage/common.py b/src/allmydata/storage/common.py
index 48fc77840..17a3f41b7 100644
--- a/src/allmydata/storage/common.py
+++ b/src/allmydata/storage/common.py
@@ -21,6 +21,12 @@ class UnknownContainerVersionError(Exception):
         self.filename = filename
         self.version = version
 
+    def __str__(self):
+        return "sharefile {!r} had unexpected version {!r}".format(
+            self.filename,
+            self.version,
+        )
+
 class UnknownMutableContainerVersionError(UnknownContainerVersionError):
     pass
 
diff --git a/src/allmydata/storage/lease.py b/src/allmydata/storage/lease.py
index 8be44bafd..c056a7d28 100644
--- a/src/allmydata/storage/lease.py
+++ b/src/allmydata/storage/lease.py
@@ -287,6 +287,10 @@ class HashedLeaseInfo(proxyForInterface(ILeaseInfo, "_lease_info")): # type: ign
     _lease_info = attr.ib()
     _hash = attr.ib()
 
+    # proxyForInterface will take care of forwarding all methods on ILeaseInfo
+    # to `_lease_info`.  Here we override a few of those methods to adjust
+    # their behavior to make them suitable for use with hashed secrets.
+
     def renew(self, new_expire_time):
         # Preserve the HashedLeaseInfo wrapper around the renewed LeaseInfo.
         return attr.assoc(
@@ -315,7 +319,7 @@ class HashedLeaseInfo(proxyForInterface(ILeaseInfo, "_lease_info")): # type: ign
         Hash the candidate secret and compare the result to the stored hashed
         secret.
         """
-        if  isinstance(candidate_secret, _HashedCancelSecret):
+        if isinstance(candidate_secret, _HashedCancelSecret):
             # Someone read it off of this object in this project - probably
             # the lease crawler - and is just trying to use it to identify
             # which lease it wants to operate on.  Avoid re-hashing the value.
diff --git a/src/allmydata/test/test_storage.py b/src/allmydata/test/test_storage.py
index 91c7adb7f..8251436d8 100644
--- a/src/allmydata/test/test_storage.py
+++ b/src/allmydata/test/test_storage.py
@@ -654,6 +654,7 @@ class Server(unittest.TestCase):
                                   ss.remote_get_buckets, b"si1")
         self.assertEqual(e.filename, fn)
         self.assertEqual(e.version, 0)
+        self.assertIn("had unexpected version 0", str(e))
 
     def test_disconnect(self):
         # simulate a disconnection
@@ -1139,6 +1140,8 @@ class MutableServer(unittest.TestCase):
                                   read, b"si1", [0], [(0,10)])
         self.assertEqual(e.filename, fn)
         self.assertTrue(e.version.startswith(b"BAD MAGIC"))
+        self.assertIn("had unexpected version", str(e))
+        self.assertIn("BAD MAGIC", str(e))
 
     def test_container_size(self):
         ss = self.create("test_container_size")