diff --git a/pyproject.toml b/pyproject.toml
index 30c4a4e..f1555a2 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -37,5 +37,12 @@ pydoc_color = "eris.pydoc_color:main"
 [project.urls]
 homepage = "https://github.com/ahamilton/eris"
 
+[build-system]
+requires = ["setuptools>=61.0"]
+build-backend = "setuptools.build_meta"
+
 [tool.setuptools]
 packages=["eris"]
+
+[tool.setuptools.package-data]
+"eris" = ["tools.toml"]