The rules limiting a driver to one helmet design per season have officially been relaxed at the most recent meeting of the FIA's World Motor Sport Council (WMSC).
The oft-derided rule requires drivers to stick to a single helmet design for the entire season to make them easier to spot for spectators.
This year a number of drivers have run one-off helmet designs at stand-alone races, with the FIA turning a blind eye to the changes as long as the design reverts to the original livery at the next round.
Now the WMSC has formalised the rule to clarify what is and what is not allowed.
"Drivers must continue to present their helmets in substantially the same livery at every event of the FIA Formula One World Championship for easy recognition of the driver in the car," a statement said.
"However, a driver will now be allowed one event [such as a home race] for a special livery [at the driver's choice].
"Drivers will also be allowed to change their helmet liveries if changing teams during the season."