diff --git a/dulwich/tests/test_greenthreads.py b/dulwich/tests/test_greenthreads.py
index 33ae0599..c3821fed 100644
--- a/dulwich/tests/test_greenthreads.py
+++ b/dulwich/tests/test_greenthreads.py
@@ -1,134 +1,134 @@
 # test_greenthreads.py -- Unittests for eventlet.
 # Copyright (C) 2013 eNovance SAS <licensing@enovance.com>
 #
 # Author: Fabien Boucher <fabien.boucher@enovance.com>
 #
 # This program is free software; you can redistribute it and/or
 # modify it under the terms of the GNU General Public License
 # as published by the Free Software Foundation; version 2
 # of the License or (at your option) any later version of
 # the License.
 #
 # This program is distributed in the hope that it will be useful,
 # but WITHOUT ANY WARRANTY; without even the implied warranty of
 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 # GNU General Public License for more details.
 #
 # You should have received a copy of the GNU General Public License
 # along with this program; if not, write to the Free Software
 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
 # MA  02110-1301, USA.
 
 import time
 
 from dulwich.tests import (
     skipIf,
     TestCase,
     )
 from dulwich.object_store import (
     MemoryObjectStore,
     MissingObjectFinder,
     )
 from dulwich.objects import (
     Commit,
     Blob,
     Tree,
     parse_timezone,
     )
 
 try:
     import gevent
     gevent_support = True
 except ImportError:
     gevent_support = False
 
 if gevent_support:
     from dulwich.greenthreads import (
         GreenThreadsObjectStoreIterator,
         GreenThreadsMissingObjectFinder,
     )
 
 skipmsg = "Gevent library is not installed"
 
 def create_commit(marker=None):
-    blob = Blob.from_string(b'The blob content %s' % marker)
+    blob = Blob.from_string(b'The blob content ' + marker)
     tree = Tree()
-    tree.add(b"thefile %s" % marker, 0o100644, blob.id)
+    tree.add(b"thefile " + marker, 0o100644, blob.id)
     cmt = Commit()
     cmt.tree = tree.id
     cmt.author = cmt.committer = b"John Doe <john@doe.net>"
     cmt.message = marker
     tz = parse_timezone(b'-0200')[0]
     cmt.commit_time = cmt.author_time = int(time.time())
     cmt.commit_timezone = cmt.author_timezone = tz
     return cmt, tree, blob
 
 
 def init_store(store, count=1):
     ret = []
     for i in range(0, count):
         objs = create_commit(marker=("%d" % i).encode('ascii'))
         for obj in objs:
             ret.append(obj)
             store.add_object(obj)
     return ret
 
 
 @skipIf(not gevent_support, skipmsg)
 class TestGreenThreadsObjectStoreIterator(TestCase):
 
     def setUp(self):
         super(TestGreenThreadsObjectStoreIterator, self).setUp()
         self.store = MemoryObjectStore()
         self.cmt_amount = 10
         self.objs = init_store(self.store, self.cmt_amount)
 
     def test_len(self):
         wants = [sha.id for sha in self.objs if isinstance(sha, Commit)]
         finder = MissingObjectFinder(self.store, (), wants)
         iterator = GreenThreadsObjectStoreIterator(self.store,
                                                iter(finder.next, None),
                                                finder)
         # One commit refers one tree and one blob
         self.assertEqual(len(iterator), self.cmt_amount * 3)
         haves = wants[0:self.cmt_amount-1]
         finder = MissingObjectFinder(self.store, haves, wants)
         iterator = GreenThreadsObjectStoreIterator(self.store,
                                                iter(finder.next, None),
                                                finder)
         self.assertEqual(len(iterator), 3)
 
     def test_iter(self):
         wants = [sha.id for sha in self.objs if isinstance(sha, Commit)]
         finder = MissingObjectFinder(self.store, (), wants)
         iterator = GreenThreadsObjectStoreIterator(self.store,
                                                iter(finder.next, None),
                                                finder)
         objs = []
         for sha, path in iterator:
             self.assertIn(sha, self.objs)
             objs.append(sha)
         self.assertEqual(len(objs), len(self.objs))
 
 
 @skipIf(not gevent_support, skipmsg)
 class TestGreenThreadsMissingObjectFinder(TestCase):
 
     def setUp(self):
         super(TestGreenThreadsMissingObjectFinder, self).setUp()
         self.store = MemoryObjectStore()
         self.cmt_amount = 10
         self.objs = init_store(self.store, self.cmt_amount)
 
     def test_finder(self):
         wants = [sha.id for sha in self.objs if isinstance(sha, Commit)]
         finder = GreenThreadsMissingObjectFinder(self.store, (), wants)
         self.assertEqual(len(finder.sha_done), 0)
         self.assertEqual(len(finder.objects_to_send), self.cmt_amount)
 
         finder = GreenThreadsMissingObjectFinder(self.store,
                                              wants[0:int(self.cmt_amount/2)],
                                              wants)
         # sha_done will contains commit id and sha of blob refered in tree
         self.assertEqual(len(finder.sha_done), (self.cmt_amount/2)*2)
         self.assertEqual(len(finder.objects_to_send), self.cmt_amount/2)