diff --git a/mitmproxy/cmdline.py b/mitmproxy/cmdline.py
index 77cdb8caa..d46051a23 100644
--- a/mitmproxy/cmdline.py
+++ b/mitmproxy/cmdline.py
@@ -9,6 +9,7 @@ import configargparse
 from mitmproxy import filt
 from mitmproxy.proxy import config
 from netlib import human
+from netlib import strutils
 from netlib import tcp
 from netlib import version
 from netlib.http import url
@@ -73,7 +74,7 @@ def parse_replace_hook(s):
     try:
         re.compile(regex)
     except re.error as e:
-        raise ParseException("Malformed replacement regex: %s" % str(e.message))
+        raise ParseException("Malformed replacement regex: %s" % str(e))
     return patt, regex, replacement
 
 
@@ -109,7 +110,7 @@ def parse_setheader(s):
 def parse_server_spec(spec):
     try:
         p = url.parse(spec)
-        if p[0] not in ("http", "https"):
+        if p[0] not in (b"http", b"https"):
             raise ValueError()
     except ValueError:
         raise configargparse.ArgumentTypeError(
@@ -127,7 +128,7 @@ def parse_upstream_auth(auth):
         raise configargparse.ArgumentTypeError(
             "Invalid upstream auth specification: %s" % auth
         )
-    return "Basic" + " " + base64.b64encode(auth)
+    return b"Basic" + b" " + base64.b64encode(strutils.always_bytes(auth))
 
 
 def get_common_options(options):
@@ -147,13 +148,13 @@ def get_common_options(options):
         try:
             p = parse_replace_hook(i)
         except ParseException as e:
-            raise configargparse.ArgumentTypeError(e.message)
+            raise configargparse.ArgumentTypeError(e)
         reps.append(p)
     for i in options.replace_file:
         try:
             patt, rex, path = parse_replace_hook(i)
         except ParseException as e:
-            raise configargparse.ArgumentTypeError(e.message)
+            raise configargparse.ArgumentTypeError(e)
         try:
             v = open(path, "rb").read()
         except IOError as e:
@@ -167,7 +168,7 @@ def get_common_options(options):
         try:
             p = parse_setheader(i)
         except ParseException as e:
-            raise configargparse.ArgumentTypeError(e.message)
+            raise configargparse.ArgumentTypeError(e)
         setheaders.append(p)
 
     if options.outfile and options.outfile[0] == options.rfile:
diff --git a/test/mitmproxy/test_cmdline.py b/test/mitmproxy/test_cmdline.py
index e75b7baf0..4fe2cf94f 100644
--- a/test/mitmproxy/test_cmdline.py
+++ b/test/mitmproxy/test_cmdline.py
@@ -39,11 +39,11 @@ def test_parse_replace_hook():
 def test_parse_server_spec():
     tutils.raises("Invalid server specification", cmdline.parse_server_spec, "")
     assert cmdline.parse_server_spec(
-        "http://foo.com:88") == ("http", ("foo.com", 88))
+        "http://foo.com:88") == (b"http", (b"foo.com", 88))
     assert cmdline.parse_server_spec(
-        "http://foo.com") == ("http", ("foo.com", 80))
+        "http://foo.com") == (b"http", (b"foo.com", 80))
     assert cmdline.parse_server_spec(
-        "https://foo.com") == ("https", ("foo.com", 443))
+        "https://foo.com") == (b"https", (b"foo.com", 443))
     tutils.raises(
         "Invalid server specification",
         cmdline.parse_server_spec,
@@ -59,9 +59,9 @@ def test_parse_upstream_auth():
     tutils.raises("Invalid upstream auth specification", cmdline.parse_upstream_auth, ":")
     tutils.raises("Invalid upstream auth specification", cmdline.parse_upstream_auth, ":test")
     assert cmdline.parse_upstream_auth(
-        "test:test") == "Basic" + " " + base64.b64encode("test:test")
+        "test:test") == b"Basic" + b" " + base64.b64encode(b"test:test")
     assert cmdline.parse_upstream_auth(
-        "test:") == "Basic" + " " + base64.b64encode("test:")
+        "test:") == b"Basic" + b" " + base64.b64encode(b"test:")
 
 
 def test_parse_setheaders():
@@ -124,7 +124,7 @@ def test_common():
     opts.replace_file = [("/foo/bar/%s" % p)]
     v = cmdline.get_common_options(opts)["replacements"]
     assert len(v) == 1
-    assert v[0][2].strip() == "replacecontents"
+    assert v[0][2].strip() == b"replacecontents"
 
 
 def test_mitmproxy():
diff --git a/tox.ini b/tox.ini
index 846078fcb..4837d5b51 100644
--- a/tox.ini
+++ b/tox.ini
@@ -7,7 +7,7 @@ deps =
   codecov>=2.0.5
 passenv = CI TRAVIS_BUILD_ID TRAVIS TRAVIS_BRANCH TRAVIS_JOB_NUMBER TRAVIS_PULL_REQUEST TRAVIS_JOB_ID TRAVIS_REPO_SLUG TRAVIS_COMMIT
 setenv =
-    PY3TESTS =  test/netlib test/pathod/ test/mitmproxy/script test/mitmproxy/test_contentview.py test/mitmproxy/test_custom_contentview.py test/mitmproxy/test_app.py test/mitmproxy/test_controller.py test/mitmproxy/test_fuzzing.py test/mitmproxy/test_script.py test/mitmproxy/test_web_app.py test/mitmproxy/test_utils.py test/mitmproxy/test_stateobject.py
+    PY3TESTS =  test/netlib test/pathod/ test/mitmproxy/script test/mitmproxy/test_contentview.py test/mitmproxy/test_custom_contentview.py test/mitmproxy/test_app.py test/mitmproxy/test_controller.py test/mitmproxy/test_fuzzing.py test/mitmproxy/test_script.py test/mitmproxy/test_web_app.py test/mitmproxy/test_utils.py test/mitmproxy/test_stateobject.py test/mitmproxy/test_cmdline.py
 
 [testenv:py27]
 commands =