diff --git a/quamash/__init__.py b/quamash/__init__.py
index 5a357cf..cfd2ea2 100644
--- a/quamash/__init__.py
+++ b/quamash/__init__.py
@@ -347,10 +347,14 @@ def call_later(self, delay, callback, *args):
 
 	def _add_callback(self, handle, delay=0):
 		def upon_timeout():
+			nonlocal timer
+			nonlocal handle
 			assert timer in self.__timers, 'Timer {} not among {}'.format(timer, self.__timers)
 			self.__timers.remove(timer)
+			timer = None
 			self._logger.debug('Callback timer fired, calling {}'.format(handle))
 			handle._run()
+			handle = None
 
 		self._logger.debug('Adding callback {} with delay {}'.format(handle, delay))
 		timer = QtCore.QTimer(self.__app)
diff --git a/tests/test_qeventloop.py b/tests/test_qeventloop.py
index 7fadb24..0b3474a 100644
--- a/tests/test_qeventloop.py
+++ b/tests/test_qeventloop.py
@@ -691,7 +691,7 @@ def fut_cb(fut):
 
 
 @pytest.mark.parametrize('use_quamash',
-	[pytest.mark.xfail(True, reason="bug34"), False]
+	[True, False]
 )
 def test_exception_handler(use_quamash, loop):
 	handler_called = False