When Elon Musk first revealed the futuristic, stainless steel-bodied Cybertruck in 2019, he boasted that it was “literally bulletproof” and made of “ultrahard” metal that was nearly impervious to dents and damage. But now, over two years later as some of the first Cybertruck deliveries begin, a worrying trend is emerging – the trucks are starting to show signs of rust from exposure to rain.

On the Cybertruck Owners Club forum, a Tesla enthusiasts community, several owners have recently posted about finding rust spots on their new vehicles after just a brief exposure to precipitation.

Raxar says the Tesla delivery specialist specifically warned them when picking up the car to avoid rain, saying the Cybertruck was prone to developing “orange rust marks” that would require buffing out. Another owner named Vertigo3pc in Los Angeles says after one spell of rain, they noticed similar corrosion forming on their Cybertruck in various spots. They brought it into a Tesla service center, where the rust was documented and confirmed.

This apparent Achilles’ heel in the Cybertruck’s armor plating comes as a surprise, given Elon Musk’s bold claims that the vehicle’s steel body was virtually impervious to damage. Stainless steel is generally highly rust-resistant, but it can deteriorate over time, especially when exposed to corrosive substances, heat, or environmental factors. And despite Musk’s assertions, the Cybertruck does not appear to have a protective clear-coat finish on its exterior that could help repel water and oxidation.

According to alleged Cybertruck owner’s manual pages leaked online recently (another one), Tesla actually warns against exposing the vehicle’s bare steel to anything that could cause corrosion, including bird droppings, tree sap, road salt, and more. This suggests the automaker is aware of the truck’s susceptibility to rust, even if it hasn’t been highlighted in marketing materials hyping the Cybertruck’s durability.

Some experts say minor surface rust on a brand-new vehicle is not necessarily alarming but can be a sign of a larger underlying issue. If left untreated, the rust spots could eventually lead to corrosion holes, flakes, and structural weakness. It’s an issue Tesla will have to stay on top of, perhaps by offering rust-proofing options to Cybertruck buyers in wet climates.

For now, the reports of rusting Cybertrucks are limited to a few owners on online forums. But as more of the trucks hit the roads in the coming year, the problem could prove more widespread. The last thing Tesla wants is for its “bulletproof” stainless steel beast to be eaten away by rust after just a few years on the road. Musk and company better get busy figuring out a corrosion solution fast, or the Cybertruck’s durability claims could prove to be all hat and no cattle.