diff --git a/src/allmydata/immutable/checker.py b/src/allmydata/immutable/checker.py
index ce533b969..2bed90e1c 100644
--- a/src/allmydata/immutable/checker.py
+++ b/src/allmydata/immutable/checker.py
@@ -616,7 +616,7 @@ class Checker(log.PrefixingLogMixin):
         d.addCallback(_got_ueb)
 
         def _discard_result(r):
-            assert isinstance(r, str), r
+            assert isinstance(r, bytes), r
             # to free up the RAM
             return None
 
diff --git a/src/allmydata/test/test_checker.py b/src/allmydata/test/test_checker.py
index 882356aeb..3ae1cc822 100644
--- a/src/allmydata/test/test_checker.py
+++ b/src/allmydata/test/test_checker.py
@@ -1,3 +1,5 @@
+from future.utils import PY2
+from past.builtins import unicode
 
 import json
 import os.path, shutil
@@ -7,7 +9,14 @@ from bs4 import BeautifulSoup
 from twisted.trial import unittest
 from twisted.internet import defer
 
-from nevow.inevow import IRequest
+# We need to use `nevow.inevow.IRequest` for now for compatibility
+# with the code in web/common.py.  Once nevow bits are gone from
+# web/common.py, we can use `twisted.web.iweb.IRequest` here.
+if PY2:
+    from nevow.inevow import IRequest
+else:
+    from twisted.web.iweb import IRequest
+
 from zope.interface import implementer
 from twisted.web.server import Request
 from twisted.web.test.requesthelper import DummyChannel
@@ -102,7 +111,7 @@ class FakeCheckResults(object):
 
     def get_corrupt_shares(self):
         # returns a list of (IServer, storage_index, sharenum)
-        return [(FakeServer(), "<fake-si>", 0)]
+        return [(FakeServer(), b"<fake-si>", 0)]
 
 
 @implementer(ICheckAndRepairResults)
@@ -141,13 +150,13 @@ class WebResultsRendering(unittest.TestCase):
         sb = StorageFarmBroker(True, None, EMPTY_CLIENT_CONFIG)
         # s.get_name() (the "short description") will be "v0-00000000".
         # s.get_longname() will include the -long suffix.
-        servers = [("v0-00000000-long", "\x00"*20, "peer-0"),
-                   ("v0-ffffffff-long", "\xff"*20, "peer-f"),
-                   ("v0-11111111-long", "\x11"*20, "peer-11")]
+        servers = [(b"v0-00000000-long", b"\x00"*20, "peer-0"),
+                   (b"v0-ffffffff-long", b"\xff"*20, "peer-f"),
+                   (b"v0-11111111-long", b"\x11"*20, "peer-11")]
         for (key_s, binary_tubid, nickname) in servers:
             server_id = key_s
             tubid_b32 = base32.b2a(binary_tubid)
-            furl = "pb://%s@nowhere/fake" % tubid_b32
+            furl = b"pb://%s@nowhere/fake" % tubid_b32
             ann = { "version": 0,
                     "service-name": "storage",
                     "anonymous-storage-FURL": furl,
@@ -174,11 +183,11 @@ class WebResultsRendering(unittest.TestCase):
         lcr = web_check_results.LiteralCheckResultsRendererElement()
 
         html = self.render_element(lcr)
-        self.failUnlessIn("Literal files are always healthy", html)
+        self.failUnlessIn(b"Literal files are always healthy", html)
 
         html = self.render_element(lcr, args={"return_to": ["FOOURL"]})
-        self.failUnlessIn("Literal files are always healthy", html)
-        self.failUnlessIn('<a href="FOOURL">Return to file.</a>', html)
+        self.failUnlessIn(b"Literal files are always healthy", html)
+        self.failUnlessIn(b'<a href="FOOURL">Return to file.</a>', html)
 
         c = self.create_fake_client()
         lcr = web_check_results.LiteralCheckResultsRenderer(c)
@@ -196,7 +205,7 @@ class WebResultsRendering(unittest.TestCase):
         serverid_f = "\xff"*20
         server_1 = sb.get_stub_server(serverid_1)
         server_f = sb.get_stub_server(serverid_f)
-        u = uri.CHKFileURI("\x00"*16, "\x00"*32, 3, 10, 1234)
+        u = uri.CHKFileURI(b"\x00"*16, b"\x00"*32, 3, 10, 1234)
         data = { "count_happiness": 8,
                  "count_shares_needed": 3,
                  "count_shares_expected": 9,
@@ -301,9 +310,9 @@ class WebResultsRendering(unittest.TestCase):
     def test_check_and_repair(self):
         c = self.create_fake_client()
         sb = c.storage_broker
-        serverid_1 = "\x00"*20
-        serverid_f = "\xff"*20
-        u = uri.CHKFileURI("\x00"*16, "\x00"*32, 3, 10, 1234)
+        serverid_1 = b"\x00"*20
+        serverid_f = b"\xff"*20
+        u = uri.CHKFileURI(b"\x00"*16, b"\x00"*32, 3, 10, 1234)
 
         data = { "count_happiness": 5,
                  "count_shares_needed": 3,
@@ -419,7 +428,7 @@ class WebResultsRendering(unittest.TestCase):
 
 
     def test_deep_check_renderer(self):
-        status = check_results.DeepCheckResults("fake-root-si")
+        status = check_results.DeepCheckResults(b"fake-root-si")
         status.add_check(
             FakeCheckResults("<unhealthy/unrecoverable>", False, False),
             (u"fake", u"unhealthy", u"unrecoverable")
@@ -512,7 +521,7 @@ class WebResultsRendering(unittest.TestCase):
         )
 
     def test_deep_check_and_repair_renderer(self):
-        status = check_results.DeepCheckAndRepairResults("")
+        status = check_results.DeepCheckAndRepairResults(b"")
 
         status.add_check_and_repair(
             FakeCheckAndRepairResults("attempted/success", True, True),
@@ -676,8 +685,8 @@ class BalancingAct(GridTestMixin, unittest.TestCase):
         c0.encoding_params['n'] = 4
         c0.encoding_params['k'] = 3
 
-        DATA = "data" * 100
-        d = c0.upload(Data(DATA, convergence=""))
+        DATA = b"data" * 100
+        d = c0.upload(Data(DATA, convergence=b""))
         def _stash_immutable(ur):
             self.imm = c0.create_node_from_uri(ur.get_uri())
             self.uri = self.imm.get_uri()
@@ -834,8 +843,8 @@ class TooParallel(GridTestMixin, unittest.TestCase):
                                         "max_segment_size": 5,
                                       }
             self.uris = {}
-            DATA = "data" * 100 # 400/5 = 80 blocks
-            return self.c0.upload(Data(DATA, convergence=""))
+            DATA = b"data" * 100 # 400/5 = 80 blocks
+            return self.c0.upload(Data(DATA, convergence=b""))
         d.addCallback(_start)
         def _do_check(ur):
             n = self.c0.create_node_from_uri(ur.get_uri())