According to an aspect, there is provided a functional safety, FS, watch-dog timer circuit for a computing device of a frequency converter controlling a motor. The FS watchdog timer circuit is configured to trigger a safe state of the frequency converter in response to a timer of the FS watchdog timer circuit expiring. Moreover, the FS watchdog timer circuit is configured to reset the time in response to receiving a first refresh signal from the computing device funning FS software using non-inverted logic as well as in response to receiving a second refresh signal from the computing device running the FS software using inverted logic.