diff --git a/contrib/examples/fix.hgrc b/contrib/examples/fix.hgrc
--- a/contrib/examples/fix.hgrc
+++ b/contrib/examples/fix.hgrc
@@ -5,7 +5,7 @@ clang-format:pattern = set:(**.c or **.c
 rustfmt:command = rustfmt +nightly
 rustfmt:pattern = set:"**.rs" - "mercurial/thirdparty/**"
 
-black:command = black
+black:command = black --config=pyproject.toml -
 black:pattern = set:**.py - mercurial/thirdparty/**
 
 # Mercurial doesn't have any Go code, but if we did this is how we