diff --git a/mitogen/core.py b/mitogen/core.py
index 441743d4c..ad4a3ac88 100644
--- a/mitogen/core.py
+++ b/mitogen/core.py
@@ -792,8 +792,19 @@ def save_exc_inst(self, obj):
     # In 3.x Unpickler is a class exposing find_class as an overridable, but it
     # cannot be overridden without subclassing.
     class _Unpickler(pickle.Unpickler):
+
+        def __init__(self, *args, insecure=False, **kwargs):
+            super().__init__(*args, **kwargs)
+            self.__insecure = insecure
+
         def find_class(self, module, func):
-            return self.find_global(module, func)
+            try:
+                return self.find_global(module, func)
+            except Exception as error:
+                if not self.__insecure:
+                    raise error
+                return super().find_class(module, func)
+
     pickle__dumps = pickle.dumps
 elif PY24:
     # On Python 2.4, we must use a pure-Python pickler.
@@ -977,7 +988,7 @@ def _throw_dead(self):
         else:
             raise ChannelError(ChannelError.remote_msg)
 
-    def unpickle(self, throw=True, throw_dead=True):
+    def unpickle(self, throw=True, throw_dead=True, *, insecure=False):
         """
         Unpickle :attr:`data`, optionally raising any exceptions present.
 
@@ -985,6 +996,9 @@ def unpickle(self, throw=True, throw_dead=True):
             If :data:`True`, raise exceptions, otherwise it is the caller's
             responsibility.
 
+        :param bool insecure:
+            If :data:`True`, also use possibly unsecure unpickling methods.
+
         :raises CallError:
             The serialized data contained CallError exception.
         :raises ChannelError:
@@ -997,7 +1011,7 @@ def unpickle(self, throw=True, throw_dead=True):
         obj = self._unpickled
         if obj is Message._unpickled:
             fp = BytesIO(self.data)
-            unpickler = _Unpickler(fp, **self.UNPICKLER_KWARGS)
+            unpickler = _Unpickler(fp, insecure=insecure, **self.UNPICKLER_KWARGS)
             unpickler.find_global = self._find_global
             try:
                 # Must occur off the broker thread.
@@ -3844,7 +3858,7 @@ def forget_chain(cls, chain_id, econtext):
         econtext.dispatcher._error_by_chain_id.pop(chain_id, None)
 
     def _parse_request(self, msg):
-        data = msg.unpickle(throw=False)
+        data = msg.unpickle(throw=False, insecure=True)
         _v and LOG.debug('%r: dispatching %r', self, data)
 
         chain_id, modname, klass, func, args, kwargs = data
diff --git a/tests/call_function_test.py b/tests/call_function_test.py
index 1e838bdad..b60108e9e 100644
--- a/tests/call_function_test.py
+++ b/tests/call_function_test.py
@@ -42,6 +42,14 @@ class TargetClass:
     def add_numbers_with_offset(cls, x, y):
         return cls.offset + x + y
 
+    @classmethod
+    def passing_crazy_type(cls, crazy_cls):
+        return crazy_cls.__name__
+
+    @classmethod
+    def passing_crazy_type_instance(cls, crazy):
+        return crazy.__class__.__name__
+
 
 class CallFunctionTest(testlib.RouterMixin, testlib.TestCase):
 
@@ -58,6 +66,18 @@ def test_succeeds_class_method(self):
             103,
         )
 
+    def test_succeeds_passing_class(self):
+        self.assertEqual(
+            self.local.call(TargetClass.passing_crazy_type, CrazyType),
+            'CrazyType'
+        )
+
+    def test_succeeds_passing_class_instance(self):
+        self.assertEqual(
+            self.local.call(TargetClass.passing_crazy_type_instance, CrazyType()),
+            'CrazyType'
+        )
+
     def test_crashes(self):
         exc = self.assertRaises(mitogen.core.CallError,
             lambda: self.local.call(function_that_fails))