A vague regulation was cleared up at Silverstone after Lewis Hamilton and Mark Webber were summoned by the stewards.
The pair were seen using their 'DRS' adjustable rear wings during rainy Friday practice, even though the innovation cannot be used on a wet track.
But McLaren, testing a new rear wing configuration ahead of the British grand prix, exploited a loophole in the rules that makes no mention of DRS being banned when the car is fitted with slick tyres.
"The stewards just wanted to understand so that they could tighten the wording of the regulations for the next race," Hamilton confirmed.
The stewards, including 1992 world champion Nigel Mansell, took no action against the 2008 world champion or Red Bull's Webber.