diff --git a/pyproject.toml b/pyproject.toml
index 562fd5e7ec1eafe724c9483195224d8b50674ce7..ec40a5cb831ca393b986d3e4ac950d18ecaf9709 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,3 +1,6 @@
 [build-system]
 requires = ['setuptools', 'wheel', 'scikit-build', 'cmake', 'ninja', 'requests', 'dune-common<=2.8.0.dev20201218', 'dune-grid<=2.8.0.dev20201218', 'dune-localfunctions<=2.8.0.dev20201218', 'dune-istl<=2.8.0.dev20201218']
 build-backend = 'setuptools.build_meta'
+
+[tool.black]
+line-length = 100