Apple Books (app) deprecating old .epub ebooks?

My New Year cleaning also involves going through all my old books (hard copy and online); deleting – by donating when possible – whichever I don’t plan to ever read or refer to again.

Imagine my surprise when, as I was looking through older .epub books in the Books app that I couldn’t see some of them. Popup says:

"Cannot Open “”
It is formatted incorrectly, or is not a format that Apple Books can open.

I haven’t been able to determine what these books have in common, except that they are among the older books that I’ve acquired as .epub files. I suspect, but haven’t yet been able to confirm that they all pre-date the EPUB3 standard.

[I have rather a lot of them. I became a fan of iBooks (original name of Apple Books) when it was first available in 2010. And have been using it since for my “books”, either in .epub or pdf versions. Most are not from the Apple Books store, but other publishers (Tidbits, O’Reilly before they went to a subscription model, Baen Ebooks, Smashwords, etc. etc.). Quite a few are electronic versions of books that replaced (sometimes expensively) hard copy books; freeing up a lot of shelving space in the house).]

I don’t recall ever seeing “Cannot Open … formatted incorrectly …” message ever before in iBooks or Apple Books. Only this year, after updating the Mac to Sonoma, and the iPads & iPhones to iPadOS/iOS 17. Which presumably also updated the Books app (it’s unclear to me what numbered version it is now).

I supposed it’s possible that the various & sundry tools that different ebooks publishers and authors used to create some of those books might not have been completely faithful to the EPUB2 (original standard, there was no EPUB version 1) or even EPUB3 standards (current version is either EPUB 3.2 or 3.3). And that the new Apple Books app is more exact holding old .epub books to standards?

Anybody else seeing this problem and/or know what underlying issue might be involved here?


IF those books are not from the Apple Store you can convert them to EPUB 3 in your Mac using Sigil.

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I wonder if Calibre would convert the older format EPUB to the latest?

You can use epubcheck to determine if those books are out of spec. (When you publish a book on the Books Store, Apple verifies it using this tool,)


Thanks all. My “bad” books some of the EPUB2.1 version books I’ve bought from various 3rd-party publishers outside of Apple’s Book Store. Up until sometime earlier this year, I was able to read those books in Apple Books apps (on Mac and/or iPad & iPhone).

But as I locate their .epub files and examine those with EPUBCheck, I see various technical formatting errors that violate the EPUB2 specification. Apparently those .epub files were never fully compliant with the specs, and previous versions of the Apple Books app(s) were a lot more forgiving than the current version. Which is probably a good thing – because IMHO there could be some potential security loopholes lurking in non-spec compliant .epub books.

So far, the fix for each “bad book” has been simple:

  1. Open the .epub file in Sigil
  2. Let Sigil fix file
  3. Save the fixed version

So far, Sigil has figured out on its own what needs to be fixed. Which is a Really Good thing because the .epub files aren’t files per se, but rather a directory of several different kinds of files with very specialized formats per the EPUB specs. Reading and understanding those specs – let alone trying to fix the errors in those files manually is not for the faint of heart. Upon opening such an .epub, Sigil will pop up with the message:

“This EPUB has HTML files that are not well formed or are missing a DOCTYPE, html, head, or body elements. Signal can automatically fix thes files, although this may very rarely result in minor data loss in extreme circumstances.”

“Do you want to automatically fix the files? [No|Yes]”

So far, enthusiastically clicking on Yes has automatically fixed each file.

Now I just have to go through all of my about 900 EPUB books in the Apple Books app, spot the rest that are now unreadable, download a copy of their .epub file, and run Sigil on those.

For anyone else who may find themselves with unreadable EPUB ebooks, you can check compliance with the EPUB2 and/or EPUB3 specs using any EPUBCheck-based program; most are listed at:

And Sigil – the excellent EPUB editor (and repair program) is available for Windows x64, MacOS (intel) and MacOS (Arm64) at: