CMake creates invalid zip files

The command:

$ cmake -E tar cf ../archive.zip . --format=zip

produces a zip file which can be unpacked by CMake via:

$ cmake -E tar xfv archive.zip

The verbose output is:

x ./
x ./readme.md

But Windows cannot extract the zip file, it complains as being invalid.

I assume the ./ directory and the ./ prefix is causing Windows problems.