To quote a certain flight safety manager "Fatigue is NOT a flight safety issue" - Go figure. The more he was questioned the more irrate he became.
Just to play devil's advocate, and being very pedantic, but the
consequences of fatigue may be a flight safety issue, but not being fatigued itself. If you fly when fatigued and nothing happens then there is no flight safety issue, but if you fly when fatigued, cock up and then site fatigue as the issue then you're in the wrong.
So, simple, don't fly when you're fatigued!