diff --git a/platypush/plugins/camera/pi.py b/platypush/plugins/camera/pi.py
index 6ffc10b1..e06416da 100644
--- a/platypush/plugins/camera/pi.py
+++ b/platypush/plugins/camera/pi.py
@@ -86,7 +86,7 @@ class CameraPiPlugin(CameraPlugin):
         self._time_lapse_stop_condition = threading.Condition()
         self._recording_stop_condition = threading.Condition()
         self._streaming_stop_condition = threading.Condition()
-        self._output: Optional[StreamingOutput] = None
+        self._output = None
 
     # noinspection PyUnresolvedReferences,PyPackageRequirements
     def _get_camera(self, **opts):
diff --git a/platypush/plugins/gpio/sensor/distance/__init__.py b/platypush/plugins/gpio/sensor/distance/__init__.py
index 9708b22e..4945432a 100644
--- a/platypush/plugins/gpio/sensor/distance/__init__.py
+++ b/platypush/plugins/gpio/sensor/distance/__init__.py
@@ -51,7 +51,7 @@ class GpioSensorDistancePlugin(GpioPlugin, GpioSensorPlugin):
         self.measurement_interval = measurement_interval
         self.timeout = timeout
         self.warmup_time = warmup_time
-        self._measurement_thread: Optional[threading.Thread] = None
+        self._measurement_thread = None
         self._measurement_thread_lock = threading.RLock()
         self._measurement_thread_can_run = False
         self._init_board()
diff --git a/platypush/utils/workers.py b/platypush/utils/workers.py
index 6b41626e..6e0963ce 100644
--- a/platypush/utils/workers.py
+++ b/platypush/utils/workers.py
@@ -92,7 +92,7 @@ class Workers:
         # noinspection PyArgumentList
         self._workers = [worker_type(self.request_queue, self.response_queue, *args, **kwargs)
                          for _ in range(n_workers)]
-        self.responses: list = []
+        self.responses = []
 
     def start(self):
         for wrk in self._workers: