diff --git a/scada-common/util.lua b/scada-common/util.lua
index 36761fd..bcab1b5 100644
--- a/scada-common/util.lua
+++ b/scada-common/util.lua
@@ -81,6 +81,12 @@ function new_watchdog(timeout)
         self._wd_timer = os.startTimer(self._timeout)
     end
 
+    local cancel = function ()
+        if self._wd_timer ~= nil then
+            os.cancelTimer(self._wd_timer)
+        end
+    end
+
     return {
         get_timer = get_timer,
         feed = feed
diff --git a/supervisor/session/plc.lua b/supervisor/session/plc.lua
index 810d8df..6f8cb5f 100644
--- a/supervisor/session/plc.lua
+++ b/supervisor/session/plc.lua
@@ -365,6 +365,7 @@ function new_session(id, for_reactor, in_queue, out_queue)
 
     -- close the connection
     local close = function ()
+        self.plc_conn_watchdod.cancel()
         self.connected = false
         _send_mgmt(SCADA_MGMT_TYPES.CLOSE, {})
     end