She’s a fashion rule breaker.

Heidi Klum didn’t comply with the Cannes Film Festival’s new dress code, hitting the opening ceremony in a billowy floral Elie Saab gown with a dramatic floor-grazing train — which violated one of the regulations that just went into effect.

“Voluminous outfits, in particular those with a large train, that hinder the proper flow of traffic of guests and complicate seating in the theater are not permitted,” the official charter said.

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The former “Project Runway” judge, 51, wore the light pink strapless number to the “Partir Un Jour” (Leave One Day) screening, pairing it with pointy metallic pumps and dazzling Lorraine Schwartz jewelry.

Meanwhile, Klum — who loves to strip down both on the red carpet and on her social media — was at least more covered up than she has been in the past, keeping with the second new red carpet edict.

The memo added, “For decency reasons, nudity is prohibited on the red carpet, as well as any other area of the festival.”

Bella Hadid, another Cannes favorite, arrived fairly covered up this year in a silky black Saint Laurent gown, though she did show hints of skin.

And the festival isn’t messing around with its new set of mandates. “The Festival welcoming teams will be obligated to prohibit red carpet access to anyone not respecting these rules,” the statement concluded.

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While Heidi opted to skirt the rules and arrive in a voluminous train, Halle Berry was forced to switch up her look at the last minute.

“I had an amazing dress by [Gaurav] Gupta to wear tonight, and I cannot wear it because the train’s too big,” the actress, who is serving as a judge on this year’s jury, explained yesterday earlier in the day.

“I had to make a pivot. But the nudity part I do think is probably also a good rule,” Berry, added. She instead went with a dramatic striped Jacquemus gown with a pink ruffle around the back.