I am experimenting with building my own .epub files and try to validate them using FlightCrew.

Currently it says my file is invalid because it is

Unable to find zip structure: End-of-central-directory

What could this mean what could be the reason for such a message?

1 Answer 1


That would mean your EPUB does not have a proper ZIP file structure.

You can try listing the content of your file with a normal zip unpacker, or test it with a real epubreader. If those do not complain, it could mean that FlightCrew has a bug.

  • 1
    You are right, I used 7zip after FlightCrew complained about mimetype not being the first file within the .epub. This resulted in generating a .7z file, which is indeed no valid .zip.
    – Tim
    Commented Jan 17, 2014 at 14:55

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