diff --git a/mitogen/core.py b/mitogen/core.py
index dacdb444..76baf4d3 100644
--- a/mitogen/core.py
+++ b/mitogen/core.py
@@ -722,6 +722,10 @@ class Message(object):
     #: the :class:`mitogen.select.Select` interface. Defaults to :data:`None`.
     receiver = None
 
+    HEADER_FMT = '>hLLLLLL'
+    HEADER_LEN = struct.calcsize(HEADER_FMT)
+    HEADER_MAGIC = 0x4d49  # 'MI'
+
     def __init__(self, **kwargs):
         """
         Construct a message from from the supplied `kwargs`. :attr:`src_id` and
@@ -732,6 +736,14 @@ class Message(object):
         vars(self).update(kwargs)
         assert isinstance(self.data, BytesType)
 
+    def pack(self):
+        return (
+            struct.pack(self.HEADER_FMT, self.HEADER_MAGIC, self.dst_id,
+                        self.src_id, self.auth_id, self.handle,
+                        self.reply_to or 0, len(self.data))
+            + self.data
+        )
+
     def _unpickle_context(self, context_id, name):
         return _unpickle_context(context_id, name, router=self.router)
 
@@ -930,7 +942,7 @@ def _unpickle_sender(router, context_id, dst_handle):
     if not (isinstance(router, Router) and
             isinstance(context_id, (int, long)) and context_id >= 0 and
             isinstance(dst_handle, (int, long)) and dst_handle > 0):
-        raise TypeError('cannot unpickle Sender: bad input')
+        raise TypeError('cannot unpickle Sender: bad input or missing router')
     return Sender(Context(router, context_id), dst_handle)
 
 
diff --git a/tests/serialization_test.py b/tests/context_test.py
similarity index 50%
rename from tests/serialization_test.py
rename to tests/context_test.py
index 6cf5f8b7..4bc4bd2e 100644
--- a/tests/serialization_test.py
+++ b/tests/context_test.py
@@ -8,40 +8,7 @@ from mitogen.core import b
 import testlib
 
 
-class EvilObject(object):
-    pass
-
-
-def roundtrip(v):
-    msg = mitogen.core.Message.pickled(v)
-    return mitogen.core.Message(data=msg.data).unpickle()
-
-
-class EvilObjectTest(testlib.TestCase):
-    def test_deserialization_fails(self):
-        msg = mitogen.core.Message.pickled(EvilObject())
-        e = self.assertRaises(mitogen.core.StreamError,
-            lambda: msg.unpickle()
-        )
-
-
-class BlobTest(testlib.TestCase):
-    klass = mitogen.core.Blob
-
-    # Python 3 pickle protocol 2 does weird stuff depending on whether an empty
-    # or nonempty bytes is being serialized. For non-empty, it yields a
-    # _codecs.encode() call. For empty, it yields a bytes() call.
-
-    def test_nonempty_bytes(self):
-        v = mitogen.core.Blob(b('dave'))
-        self.assertEquals(b('dave'), roundtrip(v))
-
-    def test_empty_bytes(self):
-        v = mitogen.core.Blob(b(''))
-        self.assertEquals(b(''), roundtrip(v))
-
-
-class ContextTest(testlib.RouterMixin, testlib.TestCase):
+class PickleTest(testlib.RouterMixin, testlib.TestCase):
     klass = mitogen.core.Context
 
     # Ensure Context can be round-tripped by regular pickle in addition to
diff --git a/tests/message_test.py b/tests/message_test.py
new file mode 100644
index 00000000..79deb2c6
--- /dev/null
+++ b/tests/message_test.py
@@ -0,0 +1,545 @@
+
+import sys
+import struct
+
+import mock
+import unittest2
+
+import mitogen.core
+import mitogen.master
+import testlib
+
+from mitogen.core import b
+
+
+class ConstructorTest(testlib.TestCase):
+    klass = mitogen.core.Message
+
+    def test_dst_id_default(self):
+        self.assertEquals(self.klass().dst_id, None)
+
+    def test_dst_id_explicit(self):
+        self.assertEquals(self.klass(dst_id=1111).dst_id, 1111)
+
+    @mock.patch('mitogen.context_id', 1234)
+    def test_src_id_default(self):
+        self.assertEquals(self.klass().src_id, 1234)
+
+    def test_src_id_explicit(self):
+        self.assertEquals(self.klass(src_id=4321).src_id, 4321)
+
+    @mock.patch('mitogen.context_id', 5555)
+    def test_auth_id_default(self):
+        self.assertEquals(self.klass().auth_id, 5555)
+
+    def test_auth_id_explicit(self):
+        self.assertEquals(self.klass(auth_id=2222).auth_id, 2222)
+
+    def test_handle_default(self):
+        self.assertEquals(self.klass().handle, None)
+
+    def test_handle_explicit(self):
+        self.assertEquals(self.klass(handle=1234).handle, 1234)
+
+    def test_reply_to_default(self):
+        self.assertEquals(self.klass().reply_to, None)
+
+    def test_reply_to_explicit(self):
+        self.assertEquals(self.klass(reply_to=8888).reply_to, 8888)
+
+    def test_data_default(self):
+        m = self.klass()
+        self.assertEquals(m.data, b(''))
+        self.assertTrue(isinstance(m.data, mitogen.core.BytesType))
+
+    def test_data_explicit(self):
+        m = self.klass(data=b('asdf'))
+        self.assertEquals(m.data, b('asdf'))
+        self.assertTrue(isinstance(m.data, mitogen.core.BytesType))
+
+    def test_data_hates_unicode(self):
+        self.assertRaises(Exception,
+            lambda: self.klass(data=u'asdf'))
+
+
+class PackTest(testlib.TestCase):
+    klass = mitogen.core.Message
+
+    def test_header_format_sanity(self):
+        self.assertEquals(self.klass.HEADER_LEN,
+                          struct.calcsize(self.klass.HEADER_FMT))
+
+    def test_header_length_correct(self):
+        s = self.klass(dst_id=123, handle=123).pack()
+        self.assertEquals(len(s), self.klass.HEADER_LEN)
+
+    def test_magic(self):
+        s = self.klass(dst_id=123, handle=123).pack()
+        magic, = struct.unpack('>h', s[:2])
+        self.assertEquals(self.klass.HEADER_MAGIC, magic)
+
+    def test_dst_id(self):
+        s = self.klass(dst_id=123, handle=123).pack()
+        dst_id, = struct.unpack('>L', s[2:6])
+        self.assertEquals(123, dst_id)
+
+    def test_src_id(self):
+        s = self.klass(src_id=5432, dst_id=123, handle=123).pack()
+        src_id, = struct.unpack('>L', s[6:10])
+        self.assertEquals(5432, src_id)
+
+    def test_auth_id(self):
+        s = self.klass(auth_id=1919, src_id=5432, dst_id=123, handle=123).pack()
+        auth_id, = struct.unpack('>L', s[10:14])
+        self.assertEquals(1919, auth_id)
+
+    def test_handle(self):
+        s = self.klass(dst_id=123, handle=9999).pack()
+        handle, = struct.unpack('>L', s[14:18])
+        self.assertEquals(9999, handle)
+
+    def test_reply_to(self):
+        s = self.klass(dst_id=1231, handle=7777, reply_to=9132).pack()
+        reply_to, = struct.unpack('>L', s[18:22])
+        self.assertEquals(9132, reply_to)
+
+    def test_data_length_empty(self):
+        s = self.klass(dst_id=1231, handle=7777).pack()
+        data_length, = struct.unpack('>L', s[22:26])
+        self.assertEquals(0, data_length)
+
+    def test_data_length_present(self):
+        s = self.klass(dst_id=1231, handle=7777, data=b('hello')).pack()
+        data_length, = struct.unpack('>L', s[22:26])
+        self.assertEquals(5, data_length)
+
+    def test_data_empty(self):
+        s = self.klass(dst_id=1231, handle=7777).pack()
+        data = s[26:]
+        self.assertEquals(b(''), data)
+
+    def test_data_present(self):
+        s = self.klass(dst_id=11, handle=77, data=b('hello')).pack()
+        data = s[26:]
+        self.assertEquals(b('hello'), data)
+
+
+class IsDeadTest(testlib.TestCase):
+    klass = mitogen.core.Message
+
+    def test_is_dead(self):
+        msg = self.klass(reply_to=mitogen.core.IS_DEAD)
+        self.assertTrue(msg.is_dead)
+
+    def test_is_not_dead(self):
+        msg = self.klass(reply_to=5555)
+        self.assertFalse(msg.is_dead)
+
+
+class DeadTest(testlib.TestCase):
+    klass = mitogen.core.Message
+
+    def test_no_reason(self):
+        msg = self.klass.dead()
+        self.assertEquals(msg.reply_to, mitogen.core.IS_DEAD)
+        self.assertTrue(msg.is_dead)
+        self.assertEquals(msg.data, b(''))
+
+    def test_with_reason(self):
+        msg = self.klass.dead(reason=u'oh no')
+        self.assertEquals(msg.reply_to, mitogen.core.IS_DEAD)
+        self.assertTrue(msg.is_dead)
+        self.assertEquals(msg.data, b('oh no'))
+
+
+class EvilObject(object):
+    pass
+
+
+class PickledTest(testlib.TestCase):
+    # getting_started.html#rpc-serialization-rules
+    klass = mitogen.core.Message
+
+    def roundtrip(self, v, router=None):
+        msg = self.klass.pickled(v)
+        msg2 = self.klass(data=msg.data)
+        msg2.router = router
+        return msg2.unpickle()
+
+    def test_bool(self):
+        for b in True, False:
+            self.assertEquals(b, self.roundtrip(b))
+
+    @unittest2.skipIf(condition=sys.version_info < (2, 6),
+                      reason='bytearray missing on <2.6')
+    def test_bytearray(self):
+        ba = bytearray(b('123'))
+        self.assertRaises(mitogen.core.StreamError,
+            lambda: self.roundtrip(ba)
+        )
+
+    def test_bytes(self):
+        by = b('123')
+        self.assertEquals(by, self.roundtrip(by))
+
+    def test_dict(self):
+        d = {1: 2, u'a': 3, b('b'): 4, 'c': {}}
+        roundtrip = self.roundtrip(d)
+        self.assertEquals(d, roundtrip)
+        self.assertTrue(isinstance(roundtrip, dict))
+        for k in d:
+            self.assertTrue(isinstance(roundtrip[k], type(d[k])))
+
+    def test_int(self):
+        self.assertEquals(123, self.klass.pickled(123).unpickle())
+
+    def test_list(self):
+        l = [1, u'b', b('c')]
+        roundtrip = self.roundtrip(l)
+        self.assertTrue(isinstance(roundtrip, list))
+        self.assertEquals(l, roundtrip)
+        for k in range(len(l)):
+            self.assertTrue(isinstance(roundtrip[k], type(l[k])))
+
+    @unittest2.skipIf(condition=sys.version_info > (3, 0),
+                      reason='long missing in >3.x')
+    def test_long(self):
+        l = long(0xffffffffffff)
+        roundtrip = self.roundtrip(l)
+        self.assertEquals(l, roundtrip)
+        self.assertTrue(isinstance(roundtrip, long))
+
+    def test_tuple(self):
+        l = (1, u'b', b('c'))
+        roundtrip = self.roundtrip(l)
+        self.assertEquals(l, roundtrip)
+        self.assertTrue(isinstance(roundtrip, tuple))
+        for k in range(len(l)):
+            self.assertTrue(isinstance(roundtrip[k], type(l[k])))
+
+    def test_unicode(self):
+        u = u'abcd'
+        roundtrip = self.roundtrip(u)
+        self.assertEquals(u, roundtrip)
+        self.assertTrue(isinstance(roundtrip, mitogen.core.UnicodeType))
+
+    #### custom types. see also: types_test.py, call_error_test.py
+
+    # Python 3 pickle protocol 2 does weird stuff depending on whether an empty
+    # or nonempty bytes is being serialized. For non-empty, it yields a
+    # _codecs.encode() call. For empty, it yields a bytes() call.
+
+    def test_blob_nonempty(self):
+        v = mitogen.core.Blob(b('dave'))
+        roundtrip = self.roundtrip(v)
+        self.assertTrue(isinstance(roundtrip, mitogen.core.Blob))
+        self.assertEquals(b('dave'), roundtrip)
+
+    def test_blob_empty(self):
+        v = mitogen.core.Blob(b(''))
+        roundtrip = self.roundtrip(v)
+        self.assertTrue(isinstance(roundtrip, mitogen.core.Blob))
+        self.assertEquals(b(''), v)
+
+    def test_secret_nonempty(self):
+        s = mitogen.core.Secret(u'dave')
+        roundtrip = self.roundtrip(s)
+        self.assertTrue(isinstance(roundtrip, mitogen.core.Secret))
+        self.assertEquals(u'dave', roundtrip)
+
+    def test_secret_empty(self):
+        s = mitogen.core.Secret(u'')
+        roundtrip = self.roundtrip(s)
+        self.assertTrue(isinstance(roundtrip, mitogen.core.Secret))
+        self.assertEquals(u'', roundtrip)
+
+    def test_call_error(self):
+        ce = mitogen.core.CallError('nope')
+        ce2 = self.assertRaises(mitogen.core.CallError,
+            lambda: self.roundtrip(ce))
+        self.assertEquals(ce.args[0], ce2.args[0])
+
+    def test_context(self):
+        router = mitogen.master.Router()
+        try:
+            c = router.context_by_id(1234)
+            roundtrip = self.roundtrip(c)
+            self.assertTrue(isinstance(roundtrip, mitogen.core.Context))
+            self.assertEquals(c.context_id, 1234)
+        finally:
+            router.broker.shutdown()
+            router.broker.join()
+
+    def test_sender(self):
+        router = mitogen.master.Router()
+        try:
+            recv = mitogen.core.Receiver(router)
+            sender = recv.to_sender()
+            roundtrip = self.roundtrip(sender, router=router)
+            self.assertTrue(isinstance(roundtrip, mitogen.core.Sender))
+            self.assertEquals(roundtrip.context.context_id, mitogen.context_id)
+            self.assertEquals(roundtrip.dst_handle, sender.dst_handle)
+        finally:
+            router.broker.shutdown()
+            router.broker.join()
+
+    ####
+
+    def test_custom_object_deserialization_fails(self):
+        self.assertRaises(mitogen.core.StreamError,
+            lambda: self.roundtrip(EvilObject())
+        )
+
+
+class ReplyTest(testlib.TestCase):
+    # getting_started.html#rpc-serialization-rules
+    klass = mitogen.core.Message
+
+    def test_reply_calls_router_route(self):
+        msg = self.klass(src_id=1234, reply_to=9191)
+        router = mock.Mock()
+        msg.reply(123, router=router)
+        self.assertEquals(1, router.route.call_count)
+
+    def test_reply_pickles_object(self):
+        msg = self.klass(src_id=1234, reply_to=9191)
+        router = mock.Mock()
+        msg.reply(123, router=router)
+        _, (reply,), _ = router.route.mock_calls[0]
+        self.assertEquals(reply.dst_id, 1234)
+        self.assertEquals(reply.unpickle(), 123)
+
+    def test_reply_uses_preformatted_message(self):
+        msg = self.klass(src_id=1234, reply_to=9191)
+        router = mock.Mock()
+        my_reply = mitogen.core.Message.pickled(4444)
+        msg.reply(my_reply, router=router)
+        _, (reply,), _ = router.route.mock_calls[0]
+        self.assertTrue(my_reply is reply)
+        self.assertEquals(reply.dst_id, 1234)
+        self.assertEquals(reply.unpickle(), 4444)
+
+    def test_reply_sets_dst_id(self):
+        msg = self.klass(src_id=1234, reply_to=9191)
+        router = mock.Mock()
+        msg.reply(123, router=router)
+        _, (reply,), _ = router.route.mock_calls[0]
+        self.assertEquals(reply.dst_id, 1234)
+
+    def test_reply_sets_handle(self):
+        msg = self.klass(src_id=1234, reply_to=9191)
+        router = mock.Mock()
+        msg.reply(123, router=router)
+        _, (reply,), _ = router.route.mock_calls[0]
+        self.assertEquals(reply.handle, 9191)
+
+
+class UnpickleTest(testlib.TestCase):
+    # mostly done by PickleTest, just check behaviour of parameters
+    klass = mitogen.core.Message
+
+    def test_throw(self):
+        ce = mitogen.core.CallError('nope')
+        m = self.klass.pickled(ce)
+        ce2 = self.assertRaises(mitogen.core.CallError,
+            lambda: m.unpickle())
+        self.assertEquals(ce.args[0], ce2.args[0])
+
+    def test_no_throw(self):
+        ce = mitogen.core.CallError('nope')
+        m = self.klass.pickled(ce)
+        ce2 = m.unpickle(throw=False)
+        self.assertEquals(ce.args[0], ce2.args[0])
+
+    def test_throw_dead(self):
+        m = self.klass.pickled('derp', reply_to=mitogen.core.IS_DEAD)
+        self.assertRaises(mitogen.core.ChannelError,
+            lambda: m.unpickle())
+
+    def test_no_throw_dead(self):
+        m = self.klass.pickled('derp', reply_to=mitogen.core.IS_DEAD)
+        self.assertEquals('derp', m.unpickle(throw_dead=False))
+
+
+class UnpickleCompatTest(testlib.TestCase):
+    # try weird variations of pickles from different Python versions.
+    klass = mitogen.core.Message
+
+    def check(self, value, encoded, **kwargs):
+        if isinstance(encoded, mitogen.core.UnicodeType):
+            encoded = encoded.encode('latin1')
+        m = self.klass(data=encoded)
+        m.router = mitogen.master.Router()
+        try:
+            return m.unpickle(**kwargs)
+        finally:
+            m.router.broker.shutdown()
+            m.router.broker.join()
+
+    def test_py24_bytes(self):
+        self.check('test',
+           ('\x80\x02U\x04testq\x00.'))
+
+    def test_py24_unicode(self):
+        self.check(u'test',
+           ('\x80\x02X\x04\x00\x00\x00testq\x00.'))
+
+    def test_py24_int(self):
+        self.check(123,
+           ('\x80\x02K{.'))
+
+    def test_py24_long(self):
+        self.check(17592186044415,
+           ('\x80\x02\x8a\x06\xff\xff\xff\xff\xff\x0f.'))
+
+    def test_py24_dict(self):
+        self.check({},
+           ('\x80\x02}q\x00.'))
+
+    def test_py24_tuple(self):
+        self.check((1, 2, u'b'),
+           ('\x80\x02K\x01K\x02X\x01\x00\x00\x00bq\x00\x87q\x01.'))
+
+    def test_py24_bool(self):
+        self.check(True,
+           ('\x80\x02\x88.'))
+
+    def test_py24_list(self):
+        self.check([1, 2, u'b'],
+           ('\x80\x02]q\x00(K\x01K\x02X\x01\x00\x00\x00bq\x01e.'))
+
+    def test_py24_blob(self):
+        self.check(mitogen.core.mitogen.core.Blob(b('bigblob')),
+           ('\x80\x02cmitogen.core\nBlob\nq\x00U\x07bigblobq\x01\x85q\x02Rq\x03.'))
+
+    def test_py24_secret(self):
+        self.check(mitogen.core.Secret(u'mypassword'),
+           ('\x80\x02cmitogen.core\nSecret\nq\x00X\n\x00\x00\x00mypasswordq\x01\x85q\x02Rq\x03.'))
+
+    def test_py24_call_error(self):
+        self.check(mitogen.core.CallError('big error'),
+           ('\x80\x02cmitogen.core\n_unpickle_call_error\nq\x00X\t\x00\x00\x00big errorq\x01\x85q\x02R.'), throw=False)
+
+    def test_py24_context(self):
+        self.check(mitogen.core.Context(1234, None),
+           ('\x80\x02cmitogen.core\n_unpickle_context\nq\x00M\xd2\x04N\x86q\x01Rq\x02.'))
+
+    def test_py24_sender(self):
+        self.check(mitogen.core.Sender(mitogen.core.Context(55555, None), 4444),
+           ('\x80\x02cmitogen.core\n_unpickle_sender\nq\x00M\x03\xd9M\\\x11\x86q\x01Rq\x02.'))
+
+    def test_py27_bytes(self):
+        self.check(b('test'),
+           ('\x80\x02U\x04testq\x01.'))
+
+    def test_py27_unicode(self):
+        self.check(u'test',
+           ('\x80\x02X\x04\x00\x00\x00testq\x01.'))
+
+    def test_py27_int(self):
+        self.check(123,
+           ('\x80\x02K{.'))
+
+    def test_py27_long(self):
+        self.check(17592186044415,
+           ('\x80\x02\x8a\x06\xff\xff\xff\xff\xff\x0f.'))
+
+    def test_py27_dict(self):
+        self.check({},
+           ('\x80\x02}q\x01.'))
+
+    def test_py27_tuple(self):
+        self.check((1, 2, u'b'),
+           ('\x80\x02K\x01K\x02X\x01\x00\x00\x00b\x87q\x01.'))
+
+    def test_py27_bool(self):
+        self.check(True,
+           ('\x80\x02\x88.'))
+
+    def test_py27_list(self):
+        self.check([1, 2, u'b'],
+           ('\x80\x02]q\x01(K\x01K\x02X\x01\x00\x00\x00be.'))
+
+    def test_py27_blob(self):
+        self.check(mitogen.core.mitogen.core.Blob(b('bigblob')),
+           ('\x80\x02cmitogen.core\nBlob\nq\x01U\x07bigblob\x85Rq\x02.'))
+
+    def test_py27_secret(self):
+        self.check(mitogen.core.Secret(u'mypassword'),
+           ('\x80\x02cmitogen.core\nSecret\nq\x01X\n\x00\x00\x00mypassword\x85Rq\x02.'))
+
+    def test_py27_call_error(self):
+        self.check(mitogen.core.CallError(u'big error',),
+           ('\x80\x02cmitogen.core\n_unpickle_call_error\nq\x01X\t\x00\x00\x00big errorq\x02\x85Rq\x03.'), throw=False)
+
+    def test_py27_context(self):
+        self.check(mitogen.core.Context(1234, None),
+           ('\x80\x02cmitogen.core\n_unpickle_context\nq\x01M\xd2\x04N\x86Rq\x02.'))
+
+    def test_py27_sender(self):
+        self.check(mitogen.core.Sender(mitogen.core.Context(55555, None), 4444),
+           ('\x80\x02cmitogen.core\n_unpickle_sender\nq\x01M\x03\xd9M\\\x11\x86Rq\x02.'))
+
+    def test_py36_bytes(self):
+        self.check(b('test'),
+           ('\x80\x02c_codecs\nencode\nq\x00X\x04\x00\x00\x00testq\x01X\x06\x00\x00\x00latin1q\x02\x86q\x03Rq\x04.'))
+
+    def test_py36_unicode(self):
+        self.check('test',
+           ('\x80\x02X\x04\x00\x00\x00testq\x00.'))
+
+    def test_py36_int(self):
+        self.check(123,
+           ('\x80\x02K{.'))
+
+    def test_py36_long(self):
+        self.check(17592186044415,
+           ('\x80\x02\x8a\x06\xff\xff\xff\xff\xff\x0f.'))
+
+    def test_py36_dict(self):
+        self.check({},
+           ('\x80\x02}q\x00.'))
+
+    def test_py36_tuple(self):
+        self.check((1, 2, u'b'),
+           ('\x80\x02K\x01K\x02X\x01\x00\x00\x00bq\x00\x87q\x01.'))
+
+    def test_py36_bool(self):
+        self.check(True,
+           ('\x80\x02\x88.'))
+
+    def test_py36_list(self):
+        self.check([1, 2, u'b'],
+           ('\x80\x02]q\x00(K\x01K\x02X\x01\x00\x00\x00bq\x01e.'))
+
+    def test_py36_blob(self):
+        self.check(mitogen.core.mitogen.core.Blob(b('bigblob')),
+           ('\x80\x02cmitogen.core\nBlob\nq\x00c_codecs\nencode\nq\x01X\x07\x00\x00\x00bigblobq\x02X\x06\x00\x00\x00latin1q\x03\x86q\x04Rq\x05\x85q\x06Rq\x07.'))
+
+    def test_py36_secret(self):
+        self.check(mitogen.core.Secret('mypassword'),
+           ('\x80\x02cmitogen.core\nSecret\nq\x00X\n\x00\x00\x00mypasswordq\x01\x85q\x02Rq\x03.'))
+
+    def test_py36_call_error(self):
+        self.check(mitogen.core.CallError('big error'),
+           ('\x80\x02cmitogen.core\n_unpickle_call_error\nq\x00X\t\x00\x00\x00big errorq\x01\x85q\x02Rq\x03.'), throw=False)
+
+    def test_py36_context(self):
+        self.check(mitogen.core.Context(1234, None),
+           ('\x80\x02cmitogen.core\n_unpickle_context\nq\x00M\xd2\x04N\x86q\x01Rq\x02.'))
+
+    def test_py36_sender(self):
+        self.check(mitogen.core.Sender(mitogen.core.Context(55555, None), 4444),
+           ('\x80\x02cmitogen.core\n_unpickle_sender\nq\x00M\x03\xd9M\\\x11\x86q\x01Rq\x02.'))
+
+
+class ReprTest(testlib.TestCase):
+    klass = mitogen.core.Message
+
+    def test_repr(self):
+        # doesn't crash
+        repr(self.klass.pickled('test'))
+
+
+if __name__ == '__main__':
+    unittest2.main()