diff --git a/src/allmydata/immutable/checker.py b/src/allmydata/immutable/checker.py
index 9636b9a2f..c1eb5480d 100644
--- a/src/allmydata/immutable/checker.py
+++ b/src/allmydata/immutable/checker.py
@@ -477,7 +477,7 @@ class Checker(log.PrefixingLogMixin):
                  monitor):
         assert precondition(isinstance(verifycap, CHKFileVerifierURI), verifycap, type(verifycap))
 
-        prefix = "%s" % base32.b2a(verifycap.get_storage_index()[:8])[:12]
+        prefix = str(base32.b2a(verifycap.get_storage_index()[:8])[:12], "utf-8")
         log.PrefixingLogMixin.__init__(self, facility="tahoe.immutable.checker", prefix=prefix)
 
         self._verifycap = verifycap
diff --git a/src/allmydata/immutable/encode.py b/src/allmydata/immutable/encode.py
index a9835b6b8..bbb7f8123 100644
--- a/src/allmydata/immutable/encode.py
+++ b/src/allmydata/immutable/encode.py
@@ -106,7 +106,7 @@ class Encoder(object):
 
     def __repr__(self):
         if hasattr(self, "_storage_index"):
-            return "<Encoder for %s>" % si_b2a(self._storage_index)[:5]
+            return "<Encoder for %r>" % si_b2a(self._storage_index)[:5]
         return "<Encoder for unknown storage index>"
 
     def log(self, *args, **kwargs):
diff --git a/src/allmydata/immutable/upload.py b/src/allmydata/immutable/upload.py
index 46e01184f..b2c4c744d 100644
--- a/src/allmydata/immutable/upload.py
+++ b/src/allmydata/immutable/upload.py
@@ -437,7 +437,7 @@ class Tahoe2ServerSelector(log.PrefixingLogMixin):
         self._reactor = reactor
 
     def __repr__(self):
-        return "<Tahoe2ServerSelector for upload %s>" % self.upload_id
+        return "<Tahoe2ServerSelector for upload %r>" % self.upload_id
 
     def _create_trackers(self, candidate_servers, allocated_size,
                          file_renewal_secret, file_cancel_secret, create_server_tracker):
@@ -1314,7 +1314,7 @@ class CHKUploader(object):
         storage_index = encoder.get_param("storage_index")
         self._storage_index = storage_index
         upload_id = si_b2a(storage_index)[:5]
-        self.log("using storage index %s" % upload_id)
+        self.log("using storage index %r" % upload_id)
         server_selector = Tahoe2ServerSelector(
             upload_id,
             self._log_number,
diff --git a/src/allmydata/mutable/publish.py b/src/allmydata/mutable/publish.py
index 8a760c5d3..86ceb022c 100644
--- a/src/allmydata/mutable/publish.py
+++ b/src/allmydata/mutable/publish.py
@@ -127,7 +127,7 @@ class Publish(object):
         self._servermap = servermap
         self._storage_index = self._node.get_storage_index()
         self._log_prefix = prefix = si_b2a(self._storage_index)[:5]
-        num = self.log("Publish(%s): starting" % prefix, parent=None)
+        num = self.log("Publish(%r): starting" % prefix, parent=None)
         self._log_number = num
         self._running = True
         self._first_write_error = None
diff --git a/src/allmydata/mutable/servermap.py b/src/allmydata/mutable/servermap.py
index 6d8e7806a..be8033f4d 100644
--- a/src/allmydata/mutable/servermap.py
+++ b/src/allmydata/mutable/servermap.py
@@ -275,7 +275,7 @@ class ServerMap(object):
         """Take a versionid, return a string that describes it."""
         (seqnum, root_hash, IV, segsize, datalength, k, N, prefix,
          offsets_tuple) = verinfo
-        return "seq%d-%s" % (seqnum, base32.b2a(root_hash)[:4])
+        return "seq%d-%s" % (seqnum, unicode(base32.b2a(root_hash)[:4], "utf-8"))
 
     def summarize_versions(self):
         """Return a string describing which versions we know about."""
@@ -868,7 +868,7 @@ class ServermapUpdater(object):
         # ok, it's a valid verinfo. Add it to the list of validated
         # versions.
         self.log(" found valid version %d-%s from %s-sh%d: %d-%d/%d/%d"
-                 % (seqnum, base32.b2a(root_hash)[:4],
+                 % (seqnum, unicode(base32.b2a(root_hash)[:4], "utf-8"),
                     server.get_name(), shnum,
                     k, n, segsize, datalen),
                     parent=lp)
diff --git a/src/allmydata/storage/server.py b/src/allmydata/storage/server.py
index 5f2ef3ac2..5d167bb33 100644
--- a/src/allmydata/storage/server.py
+++ b/src/allmydata/storage/server.py
@@ -271,7 +271,7 @@ class StorageServer(service.MultiService, Referenceable):
         si_dir = storage_index_to_dir(storage_index)
         si_s = si_b2a(storage_index)
 
-        log.msg("storage: allocate_buckets %s" % si_s)
+        log.msg("storage: allocate_buckets %r" % si_s)
 
         # in this implementation, the lease information (including secrets)
         # goes into the share files themselves. It could also be put into a
@@ -397,7 +397,7 @@ class StorageServer(service.MultiService, Referenceable):
         start = time.time()
         self.count("get")
         si_s = si_b2a(storage_index)
-        log.msg("storage: get_buckets %s" % si_s)
+        log.msg("storage: get_buckets %r" % si_s)
         bucketreaders = {} # k: sharenum, v: BucketReader
         for shnum, filename in self._get_bucket_shares(storage_index):
             bucketreaders[shnum] = BucketReader(self, filename,
@@ -602,7 +602,7 @@ class StorageServer(service.MultiService, Referenceable):
         start = time.time()
         self.count("writev")
         si_s = si_b2a(storage_index)
-        log.msg("storage: slot_writev %s" % si_s)
+        log.msg("storage: slot_writev %r" % si_s)
         si_dir = storage_index_to_dir(storage_index)
         (write_enabler, renew_secret, cancel_secret) = secrets
         bucketdir = os.path.join(self.sharedir, si_dir)
@@ -669,7 +669,7 @@ class StorageServer(service.MultiService, Referenceable):
         start = time.time()
         self.count("readv")
         si_s = si_b2a(storage_index)
-        lp = log.msg("storage: slot_readv %s %s" % (si_s, shares),
+        lp = log.msg("storage: slot_readv %r %r" % (si_s, shares),
                      facility="tahoe.storage", level=log.OPERATIONAL)
         si_dir = storage_index_to_dir(storage_index)
         # shares exist if there is a file for them