Hello, I've noticed that lxml 5.1+ upgraded the manylinux wheels to a newer tag. The default ensurpip-bundled pip version in Python 3.6 does not support newer manylinuxes, hence it is likely that many CI systems that still test 3.6 now attempt to build lxml from sources. Since 5.2, this also fails with the old pip due to the old bundled pytoml, as indicated in a previous thread on this list. $ python3.6 -m venv venv3.6 $ venv3.6/bin/pip list Package Version ---------- ------- pip 18.1 setuptools 40.6.2 5.0.2 has a manylinux1 wheel: $ venv3.6/bin/pip install lxml==5.0.2 ... lxml-5.0.2-cp36-cp36m-manylinux_2_5_x86_64.manylinux1_x86_64.whl 5.1.0 builds from source but uses setup.py and works (with devel deps): $ venv3.6/bin/pip install lxml==5.1.0 ... lxml-5.1.0.tar.gz Running setup.py install for lxml ... 5.2.1 builds from source and will outright blow up when parsing pyproject.toml: $ venv3.6/bin/pip install lxml==5.2.1 ... lxml-5.1.0.tar.gz ... pip._vendor.pytoml.core.TomlError: /tmp/.../lxml/pyproject.toml(40, 1): msg If support for Python 3.6 is still desired, would it maybe make sense to keep building and uploading manylinux1 wheels to make it easier? -- Miro Hrončok -- Phone: +420777974800 IRC: mhroncok