diff --git a/t/integration/transport.py b/t/integration/transport.py
index ebb3accf..5a24f699 100644
--- a/t/integration/transport.py
+++ b/t/integration/transport.py
@@ -13,22 +13,17 @@ from case.skip import SkipTest
 
 from kombu import Connection
 from kombu import Exchange, Queue
-from kombu.five import range
+from kombu.five import buffer_t, range
+from kombu.utils.encoding import str_to_bytes
 
 if sys.version_info >= (2, 5):
     from hashlib import sha256 as _digest
 else:
     from sha import new as _digest  # noqa
 
-if not hasattr(string, 'letters'):
-    string.letters = string.ascii_letters
-
 
 def _nobuf(x):
-    if 'buffer' in locals():
-        return [str(i) if isinstance(i, buffer) else i for i in x]
-    else:
-        return [str(i) for i in x]
+    return [str(i) if isinstance(i, buffer_t) else i for i in x]
 
 
 def consumeN(conn, consumer, n=1, timeout=30):
@@ -167,13 +162,11 @@ class TransportCase(unittest.TestCase):
                 purged += self.purge_consumer(consumer)
 
     def _digest(self, data):
-        if isinstance(data, type(u'')):
-            data = data.encode()
-        return _digest(data).hexdigest()
+        return _digest(str_to_bytes(data)).hexdigest()
 
     def test_produce__consume_large_messages(
             self, bytes=1048576, n=10,
-            charset=string.punctuation + string.letters + string.digits):
+            charset=string.punctuation + string.ascii_letters + string.digits):
         if not self.verify_alive():
             return
         bytes = min(x for x in [bytes, self.message_size_limit] if x)