diff --git a/files/etc/gl-switch.d/sim.sh b/files/etc/gl-switch.d/sim.sh
index e972918..6e25810 100644
--- a/files/etc/gl-switch.d/sim.sh
+++ b/files/etc/gl-switch.d/sim.sh
@@ -9,7 +9,7 @@ logger -p notice -t blue-merle-toggle  "Called... ${action}"
 if [ "$action" = "on" ];then
     mcu_send_message "Blue Merle ${action}"
     echo "on" > /tmp/sim_change_switch
-    /usr/bin/blue-merle-switch
+    flock -n /tmp/blue-merle-switch.lock   /usr/bin/blue-merle-switch  ||  logger -p notice -t blue-merle-toggle  "Lockfile busy" &
 
 elif [ "$action" = "off" ];then
     mcu_send_message "Blue Merle ${action}"