diff --git a/acme/acme/client.py b/acme/acme/client.py
index 75b0bdc1a..bd97c2554 100644
--- a/acme/acme/client.py
+++ b/acme/acme/client.py
@@ -16,7 +16,6 @@ import requests
 from requests.adapters import HTTPAdapter
 from requests.utils import parse_header_links
 from requests_toolbelt.adapters.source import SourceAddressAdapter
-import six
 
 from acme import crypto_util
 from acme import errors
@@ -475,7 +474,7 @@ class Client(ClientBase):
                     exhausted.add(authzr)
 
         if exhausted or any(authzr.body.status == messages.STATUS_INVALID
-                            for authzr in six.itervalues(updated)):
+                            for authzr in updated.values()):
             raise errors.PollError(exhausted, updated)
 
         updated_authzrs = tuple(updated[authzr] for authzr in authzrs)
diff --git a/acme/acme/messages.py b/acme/acme/messages.py
index 1c9472aa7..038cda04b 100644
--- a/acme/acme/messages.py
+++ b/acme/acme/messages.py
@@ -2,7 +2,6 @@
 import json
 
 import josepy as jose
-import six
 
 from acme import challenges
 from acme import errors
diff --git a/acme/acme/util.py b/acme/acme/util.py
index b3b0d79eb..20fa455fd 100644
--- a/acme/acme/util.py
+++ b/acme/acme/util.py
@@ -1,7 +1,6 @@
 """ACME utilities."""
-import six
 
 
 def map_keys(dikt, func):
     """Map dictionary keys."""
-    return {func(key): value for key, value in six.iteritems(dikt)}
+    return {func(key): value for key, value in dikt.items()}
diff --git a/acme/setup.py b/acme/setup.py
index 056b00107..2d8716eb5 100644
--- a/acme/setup.py
+++ b/acme/setup.py
@@ -20,7 +20,6 @@ install_requires = [
     'requests[security]>=2.6.0',  # security extras added in 2.4.1
     'requests-toolbelt>=0.3.0',
     'setuptools>=39.0.1',
-    'six>=1.11.0',
 ]
 
 setuptools_known_environment_markers = (LooseVersion(setuptools_version) >= LooseVersion('36.2'))
diff --git a/acme/tests/crypto_util_test.py b/acme/tests/crypto_util_test.py
index ef76230a0..f271ad37d 100644
--- a/acme/tests/crypto_util_test.py
+++ b/acme/tests/crypto_util_test.py
@@ -8,7 +8,6 @@ import unittest
 
 import josepy as jose
 import OpenSSL
-import six
 
 from acme import errors
 import test_util
@@ -27,8 +26,6 @@ class SSLSocketAndProbeSNITest(unittest.TestCase):
 
         class _TestServer(socketserver.TCPServer):
 
-            # six.moves.* | pylint: disable=attribute-defined-outside-init,no-init
-
             def server_bind(self):  # pylint: disable=missing-docstring
                 self.socket = SSLSocket(socket.socket(),
                         certs)
@@ -62,7 +59,6 @@ class SSLSocketAndProbeSNITest(unittest.TestCase):
         self.assertRaises(errors.Error, self._probe, b'bar')
 
     def test_probe_connection_error(self):
-        # pylint has a hard time with six
         self.server.server_close()
         original_timeout = socket.getdefaulttimeout()
         try:
@@ -121,9 +117,9 @@ class PyOpenSSLCertOrReqSANTest(unittest.TestCase):
     @classmethod
     def _get_idn_names(cls):
         """Returns expected names from '{cert,csr}-idnsans.pem'."""
-        chars = [six.unichr(i) for i in itertools.chain(range(0x3c3, 0x400),
-                                                        range(0x641, 0x6fc),
-                                                        range(0x1820, 0x1877))]
+        chars = [chr(i) for i in itertools.chain(range(0x3c3, 0x400),
+                                                 range(0x641, 0x6fc),
+                                                 range(0x1820, 0x1877))]
         return [''.join(chars[i: i + 45]) + '.invalid'
                 for i in range(0, len(chars), 45)]