diff --git a/pyproject.toml b/pyproject.toml
index 8c14c2bffa..041dd74191 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -23,6 +23,8 @@ ACKNOWLEDGEMENTS,\
 [tool.ruff]
 # Exclude third-party code from linting and formatting
 extend-exclude = ["lib"]
+# Include Python source files that don't end with .py
+extend-include = ["tools/cc1"]
 line-length = 99
 target-version = "py37"