FIA technical director Charlie Whiting has again passed Mercedes' innovative rear wing as legal.
Red Bull team principal Christian Horner insisted after Sunday's Australian Grand Prix that he wanted clarification from Whiting with regard to the legality of the device.
The DRS-activated F-duct system apparently does not interfere with the car when the DRS is closed, but once opened it becomes operational, assisting with straight-line speed.
Horner, and Lotus team principal Eric Boullier especially, had declared their scepticism in the build up to the season-opener around Melbourne's Albert Park.
That was despite the fact Whiting had declared it "completely passive" ahead of the first practice session last Friday.
Doubts remained, however, although no protest was launched in the wake of the race, with Horner instead asking Whiting to again look into the matter.
Horner suggested there was "a grey area" which needed resolving before the teams spent a lot of money on copying the device.
With tomorrow's first practice looming for the Malaysian Grand Prix at the Sepang International Circuit, the FIA have confirmed to Press Association Sport that Whiting has no doubts the system is in accordance with the regulations.