Basically if you have two dependencies that depend on the same package, but depend on different versions or non-overlapping ranges of versions, Poetry's only solution is "tell the maintainers of your dependencies to update their pyproject.toml" - building your package will just fail, with no workaround other than to fork the dependencies and update pyproject.toml yourself. Yes, in principle that sounds like the right way to resolve it, but in practice there are lots of Python packages with overly narrow dependency version ranges (or that are pinned to a single version), the maintainers understandably aren't always that responsive, and forking all your dependencies isn't a great solution.