diff --git a/.travis.yml b/.travis.yml
index 370137f68..111ddb3d4 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -29,6 +29,8 @@ matrix:
       addons:
     - python: "2.7"
       env: TOXENV=lint
+    - python: "3.4"
+      env: TOXENV=mypy
     - python: "3.5"
       env: TOXENV=mypy
     - python: "2.7"
diff --git a/acme/acme/challenges.py b/acme/acme/challenges.py
index 9702a7a14..b2a4882eb 100644
--- a/acme/acme/challenges.py
+++ b/acme/acme/challenges.py
@@ -478,7 +478,7 @@ class TLSSNI01Response(KeyAuthorizationChallengeResponse):
             try:
                 cert = self.probe_cert(domain=domain, **kwargs)
             except errors.Error as error:
-                logger.debug(error, exc_info=True)
+                logger.debug(str(error), exc_info=True)
                 return False
 
         return self.verify_cert(cert)
diff --git a/acme/acme/client.py b/acme/acme/client.py
index 19615b087..7807f0ece 100644
--- a/acme/acme/client.py
+++ b/acme/acme/client.py
@@ -9,7 +9,6 @@ import time
 
 import six
 from six.moves import http_client  # pylint: disable=import-error
-
 import josepy as jose
 import OpenSSL
 import re
@@ -20,6 +19,8 @@ from acme import crypto_util
 from acme import errors
 from acme import jws
 from acme import messages
+# pylint: disable=unused-import, no-name-in-module
+from acme.magic_typing import Dict, List, Set, Text
 
 
 logger = logging.getLogger(__name__)
@@ -415,7 +416,7 @@ class Client(ClientBase):
         """
         # pylint: disable=too-many-locals
         assert max_attempts > 0
-        attempts = collections.defaultdict(int)
+        attempts = collections.defaultdict(int) # type: Dict[messages.AuthorizationResource, int]
         exhausted = set()
 
         # priority queue with datetime.datetime (based on Retry-After) as key,
@@ -529,7 +530,7 @@ class Client(ClientBase):
         :rtype: `list` of `OpenSSL.crypto.X509` wrapped in `.ComparableX509`
 
         """
-        chain = []
+        chain = [] # type: List[jose.ComparableX509]
         uri = certr.cert_chain_uri
         while uri is not None and len(chain) < max_length:
             response, cert = self._get_cert(uri)
@@ -864,7 +865,7 @@ class ClientNetwork(object):  # pylint: disable=too-many-instance-attributes
         self.account = account
         self.alg = alg
         self.verify_ssl = verify_ssl
-        self._nonces = set()
+        self._nonces = set() # type: Set[Text]
         self.user_agent = user_agent
         self.session = requests.Session()
         self._default_timeout = timeout
diff --git a/acme/acme/client_test.py b/acme/acme/client_test.py
index be08c2919..c17b83210 100644
--- a/acme/acme/client_test.py
+++ b/acme/acme/client_test.py
@@ -17,6 +17,7 @@ from acme import jws as acme_jws
 from acme import messages
 from acme import messages_test
 from acme import test_util
+from acme.magic_typing import Dict # pylint: disable=unused-import, no-name-in-module
 
 
 CERT_DER = test_util.load_vector('cert.der')
@@ -61,7 +62,8 @@ class ClientTestBase(unittest.TestCase):
         self.contact = ('mailto:cert-admin@example.com', 'tel:+12025551212')
         reg = messages.Registration(
             contact=self.contact, key=KEY.public_key())
-        self.new_reg = messages.NewRegistration(**dict(reg))
+        the_arg = dict(reg) # type: Dict
+        self.new_reg = messages.NewRegistration(**the_arg) # pylint: disable=star-args
         self.regr = messages.RegistrationResource(
             body=reg, uri='https://www.letsencrypt-demo.org/acme/reg/1')
 
diff --git a/acme/acme/crypto_util.py b/acme/acme/crypto_util.py
index 2281196eb..ad914ca60 100644
--- a/acme/acme/crypto_util.py
+++ b/acme/acme/crypto_util.py
@@ -6,11 +6,13 @@ import os
 import re
 import socket
 
-import OpenSSL
+from OpenSSL import crypto
+from OpenSSL import SSL # type: ignore # https://github.com/python/typeshed/issues/2052
 import josepy as jose
 
-
 from acme import errors
+# pylint: disable=unused-import, no-name-in-module
+from acme.magic_typing import Callable, Text, Union
 
 
 logger = logging.getLogger(__name__)
@@ -25,7 +27,7 @@ logger = logging.getLogger(__name__)
 # https://www.openssl.org/docs/ssl/SSLv23_method.html). _serve_sni
 # should be changed to use "set_options" to disable SSLv2 and SSLv3,
 # in case it's used for things other than probing/serving!
-_DEFAULT_TLSSNI01_SSL_METHOD = OpenSSL.SSL.SSLv23_METHOD  # type: ignore
+_DEFAULT_TLSSNI01_SSL_METHOD = SSL.SSLv23_METHOD  # type: ignore
 
 
 class SSLSocket(object):  # pylint: disable=too-few-public-methods
@@ -64,9 +66,9 @@ class SSLSocket(object):  # pylint: disable=too-few-public-methods
             logger.debug("Server name (%s) not recognized, dropping SSL",
                          server_name)
             return
-        new_context = OpenSSL.SSL.Context(self.method)
-        new_context.set_options(OpenSSL.SSL.OP_NO_SSLv2)
-        new_context.set_options(OpenSSL.SSL.OP_NO_SSLv3)
+        new_context = SSL.Context(self.method)
+        new_context.set_options(SSL.OP_NO_SSLv2)
+        new_context.set_options(SSL.OP_NO_SSLv3)
         new_context.use_privatekey(key)
         new_context.use_certificate(cert)
         connection.set_context(new_context)
@@ -89,18 +91,18 @@ class SSLSocket(object):  # pylint: disable=too-few-public-methods
     def accept(self):  # pylint: disable=missing-docstring
         sock, addr = self.sock.accept()
 
-        context = OpenSSL.SSL.Context(self.method)
-        context.set_options(OpenSSL.SSL.OP_NO_SSLv2)
-        context.set_options(OpenSSL.SSL.OP_NO_SSLv3)
+        context = SSL.Context(self.method)
+        context.set_options(SSL.OP_NO_SSLv2)
+        context.set_options(SSL.OP_NO_SSLv3)
         context.set_tlsext_servername_callback(self._pick_certificate_cb)
 
-        ssl_sock = self.FakeConnection(OpenSSL.SSL.Connection(context, sock))
+        ssl_sock = self.FakeConnection(SSL.Connection(context, sock))
         ssl_sock.set_accept_state()
 
         logger.debug("Performing handshake with %s", addr)
         try:
             ssl_sock.do_handshake()
-        except OpenSSL.SSL.Error as error:
+        except SSL.Error as error:
             # _pick_certificate_cb might have returned without
             # creating SSL context (wrong server name)
             raise socket.error(error)
@@ -128,7 +130,7 @@ def probe_sni(name, host, port=443, timeout=300,
     :rtype: OpenSSL.crypto.X509
 
     """
-    context = OpenSSL.SSL.Context(method)
+    context = SSL.Context(method)
     context.set_timeout(timeout)
 
     socket_kwargs = {'source_address': source_address}
@@ -145,13 +147,13 @@ def probe_sni(name, host, port=443, timeout=300,
         raise errors.Error(error)
 
     with contextlib.closing(sock) as client:
-        client_ssl = OpenSSL.SSL.Connection(context, client)
+        client_ssl = SSL.Connection(context, client)
         client_ssl.set_connect_state()
         client_ssl.set_tlsext_host_name(name)  # pyOpenSSL>=0.13
         try:
             client_ssl.do_handshake()
             client_ssl.shutdown()
-        except OpenSSL.SSL.Error as error:
+        except SSL.Error as error:
             raise errors.Error(error)
     return client_ssl.get_peer_certificate()
 
@@ -164,18 +166,18 @@ def make_csr(private_key_pem, domains, must_staple=False):
         OCSP Must Staple: https://tools.ietf.org/html/rfc7633).
     :returns: buffer PEM-encoded Certificate Signing Request.
     """
-    private_key = OpenSSL.crypto.load_privatekey(
-        OpenSSL.crypto.FILETYPE_PEM, private_key_pem)
-    csr = OpenSSL.crypto.X509Req()
+    private_key = crypto.load_privatekey(
+        crypto.FILETYPE_PEM, private_key_pem)
+    csr = crypto.X509Req()
     extensions = [
-        OpenSSL.crypto.X509Extension(
+        crypto.X509Extension(
             b'subjectAltName',
             critical=False,
             value=', '.join('DNS:' + d for d in domains).encode('ascii')
         ),
     ]
     if must_staple:
-        extensions.append(OpenSSL.crypto.X509Extension(
+        extensions.append(crypto.X509Extension(
             b"1.3.6.1.5.5.7.1.24",
             critical=False,
             value=b"DER:30:03:02:01:05"))
@@ -183,8 +185,8 @@ def make_csr(private_key_pem, domains, must_staple=False):
     csr.set_pubkey(private_key)
     csr.set_version(2)
     csr.sign(private_key, 'sha256')
-    return OpenSSL.crypto.dump_certificate_request(
-        OpenSSL.crypto.FILETYPE_PEM, csr)
+    return crypto.dump_certificate_request(
+        crypto.FILETYPE_PEM, csr)
 
 def _pyopenssl_cert_or_req_all_names(loaded_cert_or_req):
     common_name = loaded_cert_or_req.get_subject().CN
@@ -221,11 +223,12 @@ def _pyopenssl_cert_or_req_san(cert_or_req):
     parts_separator = ", "
     prefix = "DNS" + part_separator
 
-    if isinstance(cert_or_req, OpenSSL.crypto.X509):
-        func = OpenSSL.crypto.dump_certificate
+    if isinstance(cert_or_req, crypto.X509):
+        # pylint: disable=line-too-long
+        func = crypto.dump_certificate # type: Union[Callable[[int, crypto.X509Req], bytes], Callable[[int, crypto.X509], bytes]]
     else:
-        func = OpenSSL.crypto.dump_certificate_request
-    text = func(OpenSSL.crypto.FILETYPE_TEXT, cert_or_req).decode("utf-8")
+        func = crypto.dump_certificate_request
+    text = func(crypto.FILETYPE_TEXT, cert_or_req).decode("utf-8")
     # WARNING: this function does not support multiple SANs extensions.
     # Multiple X509v3 extensions of the same type is disallowed by RFC 5280.
     match = re.search(r"X509v3 Subject Alternative Name:(?: critical)?\s*(.*)", text)
@@ -252,12 +255,12 @@ def gen_ss_cert(key, domains, not_before=None,
 
     """
     assert domains, "Must provide one or more hostnames for the cert."
-    cert = OpenSSL.crypto.X509()
+    cert = crypto.X509()
     cert.set_serial_number(int(binascii.hexlify(os.urandom(16)), 16))
     cert.set_version(2)
 
     extensions = [
-        OpenSSL.crypto.X509Extension(
+        crypto.X509Extension(
             b"basicConstraints", True, b"CA:TRUE, pathlen:0"),
     ]
 
@@ -266,7 +269,7 @@ def gen_ss_cert(key, domains, not_before=None,
     cert.set_issuer(cert.get_subject())
 
     if force_san or len(domains) > 1:
-        extensions.append(OpenSSL.crypto.X509Extension(
+        extensions.append(crypto.X509Extension(
             b"subjectAltName",
             critical=False,
             value=b", ".join(b"DNS:" + d.encode() for d in domains)
@@ -281,7 +284,7 @@ def gen_ss_cert(key, domains, not_before=None,
     cert.sign(key, "sha256")
     return cert
 
-def dump_pyopenssl_chain(chain, filetype=OpenSSL.crypto.FILETYPE_PEM):
+def dump_pyopenssl_chain(chain, filetype=crypto.FILETYPE_PEM):
     """Dump certificate chain into a bundle.
 
     :param list chain: List of `OpenSSL.crypto.X509` (or wrapped in
@@ -298,7 +301,7 @@ def dump_pyopenssl_chain(chain, filetype=OpenSSL.crypto.FILETYPE_PEM):
         if isinstance(cert, jose.ComparableX509):
             # pylint: disable=protected-access
             cert = cert.wrapped
-        return OpenSSL.crypto.dump_certificate(filetype, cert)
+        return crypto.dump_certificate(filetype, cert)
 
     # assumes that OpenSSL.crypto.dump_certificate includes ending
     # newline character
diff --git a/acme/acme/crypto_util_test.py b/acme/acme/crypto_util_test.py
index 3874ba9d9..36d62b324 100644
--- a/acme/acme/crypto_util_test.py
+++ b/acme/acme/crypto_util_test.py
@@ -13,6 +13,7 @@ import OpenSSL
 
 from acme import errors
 from acme import test_util
+from acme.magic_typing import List # pylint: disable=unused-import, no-name-in-module
 
 
 class SSLSocketAndProbeSNITest(unittest.TestCase):
@@ -165,7 +166,7 @@ class RandomSnTest(unittest.TestCase):
 
     def setUp(self):
         self.cert_count = 5
-        self.serial_num = []
+        self.serial_num = [] # type: List[int]
         self.key = OpenSSL.crypto.PKey()
         self.key.generate_key(OpenSSL.crypto.TYPE_RSA, 2048)
 
diff --git a/acme/acme/magic_typing.py b/acme/acme/magic_typing.py
new file mode 100644
index 000000000..555088cf2
--- /dev/null
+++ b/acme/acme/magic_typing.py
@@ -0,0 +1,13 @@
+"""Shim class to not have to depend on typing module in prod."""
+import sys
+
+class TypingClass(object):
+    """Ignore import errors by getting anything"""
+    def __getattr__(self, name):
+        return None
+
+try:
+    # mypy doesn't respect modifying sys.modules
+    from typing import * # pylint: disable=wildcard-import, unused-wildcard-import
+except ImportError:
+    sys.modules[__name__] = TypingClass()
diff --git a/acme/acme/magic_typing_test.py b/acme/acme/magic_typing_test.py
new file mode 100644
index 000000000..23dfe3367
--- /dev/null
+++ b/acme/acme/magic_typing_test.py
@@ -0,0 +1,41 @@
+"""Tests for acme.magic_typing."""
+import sys
+import unittest
+
+import mock
+
+
+class MagicTypingTest(unittest.TestCase):
+    """Tests for acme.magic_typing."""
+    def test_import_success(self):
+        try:
+            import typing as temp_typing
+        except ImportError: # pragma: no cover
+            temp_typing = None # pragma: no cover
+        typing_class_mock = mock.MagicMock()
+        text_mock = mock.MagicMock()
+        typing_class_mock.Text = text_mock
+        sys.modules['typing'] = typing_class_mock
+        if 'acme.magic_typing' in sys.modules:
+            del sys.modules['acme.magic_typing'] # pragma: no cover
+        from acme.magic_typing import Text # pylint: disable=no-name-in-module
+        self.assertEqual(Text, text_mock)
+        del sys.modules['acme.magic_typing']
+        sys.modules['typing'] = temp_typing
+
+    def test_import_failure(self):
+        try:
+            import typing as temp_typing
+        except ImportError: # pragma: no cover
+            temp_typing = None # pragma: no cover
+        sys.modules['typing'] = None
+        if 'acme.magic_typing' in sys.modules:
+            del sys.modules['acme.magic_typing'] # pragma: no cover
+        from acme.magic_typing import Text # pylint: disable=no-name-in-module
+        self.assertTrue(Text is None)
+        del sys.modules['acme.magic_typing']
+        sys.modules['typing'] = temp_typing
+
+
+if __name__ == '__main__':
+    unittest.main()  # pragma: no cover
diff --git a/acme/acme/messages_test.py b/acme/acme/messages_test.py
index 64bc81efd..0e2d8c62d 100644
--- a/acme/acme/messages_test.py
+++ b/acme/acme/messages_test.py
@@ -6,6 +6,7 @@ import mock
 
 from acme import challenges
 from acme import test_util
+from acme.magic_typing import Dict # pylint: disable=unused-import, no-name-in-module
 
 
 CERT = test_util.load_comparable_cert('cert.der')
@@ -85,7 +86,7 @@ class ConstantTest(unittest.TestCase):
         from acme.messages import _Constant
 
         class MockConstant(_Constant):  # pylint: disable=missing-docstring
-            POSSIBLE_NAMES = {}
+            POSSIBLE_NAMES = {} # type: Dict
 
         self.MockConstant = MockConstant  # pylint: disable=invalid-name
         self.const_a = MockConstant('a')
diff --git a/acme/acme/standalone.py b/acme/acme/standalone.py
index c221f5883..a370501ee 100644
--- a/acme/acme/standalone.py
+++ b/acme/acme/standalone.py
@@ -16,6 +16,7 @@ import OpenSSL
 
 from acme import challenges
 from acme import crypto_util
+from acme.magic_typing import List # pylint: disable=unused-import, no-name-in-module
 
 
 logger = logging.getLogger(__name__)
@@ -66,8 +67,8 @@ class BaseDualNetworkedServers(object):
 
     def __init__(self, ServerClass, server_address, *remaining_args, **kwargs):
         port = server_address[1]
-        self.threads = []
-        self.servers = []
+        self.threads = [] # type: List[threading.Thread]
+        self.servers = [] # type: List[ACMEServerMixin]
 
         # Must try True first.
         # Ubuntu, for example, will fail to bind to IPv4 if we've already bound
@@ -189,7 +190,7 @@ class HTTP01RequestHandler(BaseHTTPServer.BaseHTTPRequestHandler):
 
     def __init__(self, *args, **kwargs):
         self.simple_http_resources = kwargs.pop("simple_http_resources", set())
-        socketserver.BaseRequestHandler.__init__(self, *args, **kwargs)
+        BaseHTTPServer.BaseHTTPRequestHandler.__init__(self, *args, **kwargs)
 
     def log_message(self, format, *args):  # pylint: disable=redefined-builtin
         """Log arbitrary message."""
@@ -262,7 +263,7 @@ def simple_tls_sni_01_server(cli_args, forever=True):
 
     certs = {}
 
-    _, hosts, _ = next(os.walk('.'))
+    _, hosts, _ = next(os.walk('.')) # type: ignore # https://github.com/python/mypy/issues/465
     for host in hosts:
         with open(os.path.join(host, "cert.pem")) as cert_file:
             cert_contents = cert_file.read()
diff --git a/acme/acme/standalone_test.py b/acme/acme/standalone_test.py
index 5b1b72c18..1591187e5 100644
--- a/acme/acme/standalone_test.py
+++ b/acme/acme/standalone_test.py
@@ -18,6 +18,7 @@ from acme import challenges
 from acme import crypto_util
 from acme import errors
 from acme import test_util
+from acme.magic_typing import Set # pylint: disable=unused-import, no-name-in-module
 
 
 class TLSServerTest(unittest.TestCase):
@@ -72,7 +73,7 @@ class HTTP01ServerTest(unittest.TestCase):
     def setUp(self):
         self.account_key = jose.JWK.load(
             test_util.load_vector('rsa1024_key.pem'))
-        self.resources = set()
+        self.resources = set() # type: Set
 
         from acme.standalone import HTTP01Server
         self.server = HTTP01Server(('', 0), resources=self.resources)
@@ -201,7 +202,7 @@ class HTTP01DualNetworkedServersTest(unittest.TestCase):
     def setUp(self):
         self.account_key = jose.JWK.load(
             test_util.load_vector('rsa1024_key.pem'))
-        self.resources = set()
+        self.resources = set() # type: Set
 
         from acme.standalone import HTTP01DualNetworkedServers
         self.servers = HTTP01DualNetworkedServers(('', 0), resources=self.resources)
diff --git a/acme/acme/test_util.py b/acme/acme/test_util.py
index d5d57bd27..1a0b67056 100644
--- a/acme/acme/test_util.py
+++ b/acme/acme/test_util.py
@@ -10,7 +10,7 @@ import unittest
 from cryptography.hazmat.backends import default_backend
 from cryptography.hazmat.primitives import serialization
 import josepy as jose
-import OpenSSL
+from OpenSSL import crypto
 
 
 def vector_path(*names):
@@ -39,8 +39,8 @@ def _guess_loader(filename, loader_pem, loader_der):
 def load_cert(*names):
     """Load certificate."""
     loader = _guess_loader(
-        names[-1], OpenSSL.crypto.FILETYPE_PEM, OpenSSL.crypto.FILETYPE_ASN1)
-    return OpenSSL.crypto.load_certificate(loader, load_vector(*names))
+        names[-1], crypto.FILETYPE_PEM, crypto.FILETYPE_ASN1)
+    return crypto.load_certificate(loader, load_vector(*names))
 
 
 def load_comparable_cert(*names):
@@ -51,8 +51,8 @@ def load_comparable_cert(*names):
 def load_csr(*names):
     """Load certificate request."""
     loader = _guess_loader(
-        names[-1], OpenSSL.crypto.FILETYPE_PEM, OpenSSL.crypto.FILETYPE_ASN1)
-    return OpenSSL.crypto.load_certificate_request(loader, load_vector(*names))
+        names[-1], crypto.FILETYPE_PEM, crypto.FILETYPE_ASN1)
+    return crypto.load_certificate_request(loader, load_vector(*names))
 
 
 def load_comparable_csr(*names):
@@ -71,8 +71,8 @@ def load_rsa_private_key(*names):
 def load_pyopenssl_private_key(*names):
     """Load pyOpenSSL private key."""
     loader = _guess_loader(
-        names[-1], OpenSSL.crypto.FILETYPE_PEM, OpenSSL.crypto.FILETYPE_ASN1)
-    return OpenSSL.crypto.load_privatekey(loader, load_vector(*names))
+        names[-1], crypto.FILETYPE_PEM, crypto.FILETYPE_ASN1)
+    return crypto.load_privatekey(loader, load_vector(*names))
 
 
 def skip_unless(condition, reason):  # pragma: no cover
diff --git a/mypy.ini b/mypy.ini
index aac60a2ad..2bac9249f 100644
--- a/mypy.ini
+++ b/mypy.ini
@@ -1,3 +1,6 @@
 [mypy]
 python_version = 2.7
 ignore_missing_imports = True
+
+[mypy-acme.*]
+check_untyped_defs = True
diff --git a/setup.py b/setup.py
index e674871a8..3760fd35b 100644
--- a/setup.py
+++ b/setup.py
@@ -67,6 +67,7 @@ dev_extras = [
 
 dev3_extras = [
     'mypy',
+    'typing', # for python3.4
 ]
 
 docs_extras = [