In the 2011 Canadian Grand Prix of Formula One, rain before the race wet the circuit. 30 minutes into the race, a heavy rainstorm hit the circuit and the race was red-flagged. The rain didn't stop quickly and the event was delayed for more than 2 hours, but the full distance was eventually run and was the longest race in Formula One history. To prevent a repeat, FIA rules were changed so that a four-hour race clock starts when the cars start their warm-up lap. The clock will not be stopped for any situation, effectively ending a race four hours after cars roll off, regardless of how far the race has finished.