diff --git a/nrf802154_sniffer/nrf802154_sniffer.py b/nrf802154_sniffer/nrf802154_sniffer.py
index a0d9e98..1ba9689 100755
--- a/nrf802154_sniffer/nrf802154_sniffer.py
+++ b/nrf802154_sniffer/nrf802154_sniffer.py
@@ -164,7 +164,7 @@ def stop_sig_handler(self, *args, **kwargs):
                 try:
                     thread.join(timeout=10)
                     if thread.is_alive() is True:
-                        self.logger.error("Failed to stop a thread")
+                        self.logger.error("Failed to stop thread {}".format(thread.name))
                         alive_threads.append(thread)
                 except RuntimeError:
                     # TODO: This may be called from one of threads from thread list - architecture problem
@@ -174,6 +174,11 @@ def stop_sig_handler(self, *args, **kwargs):
         else:
             self.logger.warning("Asked to stop {} while it was already stopped".format(self))
 
+        if self.serial is not None:
+            if self.serial.is_open is True:
+                self.serial.close()
+            self.serial = None
+
     @staticmethod
     def get_hex_path():
         """Helper method to get hex file path with nrf802154_sniffer firmware.