diff --git a/scrapy/downloadermiddlewares/httpproxy.py b/scrapy/downloadermiddlewares/httpproxy.py
index dda6a3d2a..8c3514fd0 100644
--- a/scrapy/downloadermiddlewares/httpproxy.py
+++ b/scrapy/downloadermiddlewares/httpproxy.py
@@ -9,7 +9,7 @@ from six.moves.urllib.parse import urlunparse
 
 from scrapy.utils.httpobj import urlparse_cached
 from scrapy.exceptions import NotConfigured
-
+from scrapy.utils.python import to_bytes
 
 class HttpProxyMiddleware(object):
 
@@ -26,7 +26,7 @@ class HttpProxyMiddleware(object):
         proxy_url = urlunparse((proxy_type or orig_type, hostport, '', '', '', ''))
 
         if user:
-            user_pass = '%s:%s' % (unquote(user), unquote(password))
+            user_pass = to_bytes('%s:%s' % (unquote(user), unquote(password)))
             creds = base64.b64encode(user_pass).strip()
         else:
             creds = None
@@ -52,4 +52,4 @@ class HttpProxyMiddleware(object):
         creds, proxy = self.proxies[scheme]
         request.meta['proxy'] = proxy
         if creds:
-            request.headers['Proxy-Authorization'] = 'Basic ' + creds
+            request.headers['Proxy-Authorization'] = b'Basic ' + creds
diff --git a/tests/py3-ignores.txt b/tests/py3-ignores.txt
index 8c883ee3c..185a278fb 100644
--- a/tests/py3-ignores.txt
+++ b/tests/py3-ignores.txt
@@ -2,8 +2,6 @@ tests/test_closespider.py
 tests/test_exporters.py
 tests/test_linkextractors_deprecated.py
 tests/test_crawl.py
-tests/test_downloadermiddleware_httpproxy.py
-tests/test_downloadermiddleware_retry.py
 tests/test_mail.py
 tests/test_pipeline_files.py
 tests/test_pipeline_images.py
@@ -23,8 +21,6 @@ scrapy/pipelines/files.py
 scrapy/linkextractors/sgml.py
 scrapy/linkextractors/regex.py
 scrapy/linkextractors/htmlparser.py
-scrapy/downloadermiddlewares/retry.py
-scrapy/downloadermiddlewares/httpproxy.py
 scrapy/downloadermiddlewares/cookies.py
 scrapy/extensions/statsmailer.py
 scrapy/extensions/memusage.py
diff --git a/tests/test_downloadermiddleware_httpproxy.py b/tests/test_downloadermiddleware_httpproxy.py
index 5b9717a89..7676b2a00 100644
--- a/tests/test_downloadermiddleware_httpproxy.py
+++ b/tests/test_downloadermiddleware_httpproxy.py
@@ -52,7 +52,7 @@ class TestDefaultHeadersMiddleware(TestCase):
         req = Request('http://scrapytest.org')
         assert mw.process_request(req, spider) is None
         self.assertEquals(req.meta, {'proxy': 'https://proxy:3128'})
-        self.assertEquals(req.headers.get('Proxy-Authorization'), 'Basic dXNlcjpwYXNz')
+        self.assertEquals(req.headers.get('Proxy-Authorization'), b'Basic dXNlcjpwYXNz')
 
     def test_proxy_auth_empty_passwd(self):
         os.environ['http_proxy'] = 'https://user:@proxy:3128'
@@ -60,7 +60,7 @@ class TestDefaultHeadersMiddleware(TestCase):
         req = Request('http://scrapytest.org')
         assert mw.process_request(req, spider) is None
         self.assertEquals(req.meta, {'proxy': 'https://proxy:3128'})
-        self.assertEquals(req.headers.get('Proxy-Authorization'), 'Basic dXNlcjo=')
+        self.assertEquals(req.headers.get('Proxy-Authorization'), b'Basic dXNlcjo=')
 
     def test_proxy_already_seted(self):
         os.environ['http_proxy'] = http_proxy = 'https://proxy.for.http:3128'
diff --git a/tests/test_downloadermiddleware_retry.py b/tests/test_downloadermiddleware_retry.py
index 20561e771..3de9399cf 100644
--- a/tests/test_downloadermiddleware_retry.py
+++ b/tests/test_downloadermiddleware_retry.py
@@ -21,20 +21,20 @@ class RetryTest(unittest.TestCase):
 
     def test_priority_adjust(self):
         req = Request('http://www.scrapytest.org/503')
-        rsp = Response('http://www.scrapytest.org/503', body='', status=503)
+        rsp = Response('http://www.scrapytest.org/503', body=b'', status=503)
         req2 = self.mw.process_response(req, rsp, self.spider)
         assert req2.priority < req.priority
 
     def test_404(self):
         req = Request('http://www.scrapytest.org/404')
-        rsp = Response('http://www.scrapytest.org/404', body='', status=404)
+        rsp = Response('http://www.scrapytest.org/404', body=b'', status=404)
 
         # dont retry 404s
         assert self.mw.process_response(req, rsp, self.spider) is rsp
 
     def test_dont_retry(self):
         req = Request('http://www.scrapytest.org/503', meta={'dont_retry': True})
-        rsp = Response('http://www.scrapytest.org/503', body='', status=503)
+        rsp = Response('http://www.scrapytest.org/503', body=b'', status=503)
 
         # first retry
         r = self.mw.process_response(req, rsp, self.spider)
@@ -56,7 +56,7 @@ class RetryTest(unittest.TestCase):
 
     def test_503(self):
         req = Request('http://www.scrapytest.org/503')
-        rsp = Response('http://www.scrapytest.org/503', body='', status=503)
+        rsp = Response('http://www.scrapytest.org/503', body=b'', status=503)
 
         # first retry
         req = self.mw.process_response(req, rsp, self.spider)