If you’re planning on buying a Windows 10 PC on July 29, the day of its launch—tough luck. Microsoft said Monday that PCs running Windows 10 won’t be on store shelves on that day, something totally unprecedented for a Windows launch.

Yusuf Mehdi, vice president of Windows and device marketing, confirmed the delay to Bloomberg. “You will see computers running with Windows 10 installed very soon after the 29th and then in the fall a whole new class of machines for the holidays,” he said in an interview.

Why won’t Windows 10 PCs be available on July 29, the official date on which the software will be sold at retail? Because Microsoft still hasn’t settled on a version of the software that it deems to be a release candidate (RTM), or good enough to send to PC makers. Microsoft has released several recent builds, all designed to fix bugs, but the company apparently doesn’t feel that it’s in a state that’s good enough to ship.

You'll still be able to buy them, though. "“A build of Windows 10 will be delivered to our OEM partners soon so they can start imaging new devices with Windows 10," a Microsoft spokeswoman said in an email. "We expect several OEM partners to have Windows 10 devices available for sale on July 29, including Lenovo, HP, Dell, and Acer with many, many more devices to follow in the coming weeks and months. We are excited to be working with our OEM partners to see Windows 10 innovations light up on these new devices.”

PC makers, in turn, will need some time to test the software and add their own applications (what some might call bloatware), a period historically measured in several weeks, if not months. With just 16 days left before the 29th, it appears that hardware makers now say they won’t have enough time to do their own due diligence and get Windows 10 PCs on store shelves by that date.

Microsoft, meanwhile, has made July 29 the date when retailers will begin selling Windows 10 in stores. In what looks now like a bit of misdirection, Microsoft has planned a series of “Update Your World” parties across the world and encouraged its own employees to go out into the community and assist with the update process.

Instead of buying a Windows 10 PC in a store, then, users will have to buy a Windows 8.1 PC and then either upgrade in the store itself or else take the machine home and do it then.

The "new class of products" that Mehdi referred to arriving in the fall are almost certainly PCs based on the Intel "Skylake" processor, which Intel has built a "wire-free" vision around, including wireless charging and display capabilities. Those chips are due in early August, with PCs to follow later.

Microsoft didn’t respond to requests for comment by press time.

Why this matters: If you’re like us, you generally serve as the “tech person” in your family, advising family members on what to buy, troubleshooting, and even assisting other family members with upgrades. This means on July 29, when Uncle Ned heads to Staples to pick up a new PC, he’ll either have to sit and wait while an employee upgrades the PC for him, or else you’ll have to babysit the process for him at his house an hour away. Missing the July 29 deadline probably won’t make a world of difference for Microsoft or even PC makers, but it could be a real headache for you and me. And ticking off customers should be the last thing Microsoft wants to do.

Updated at 2:33 PM with a statement from Microsoft.