diff --git a/python/ruff-ecosystem/ruff_ecosystem/defaults.py b/python/ruff-ecosystem/ruff_ecosystem/defaults.py
index 16db062715356..ad75701730d03 100644
--- a/python/ruff-ecosystem/ruff_ecosystem/defaults.py
+++ b/python/ruff-ecosystem/ruff_ecosystem/defaults.py
@@ -62,7 +62,17 @@
     Project(
         repo=Repository(owner="scikit-build", name="scikit-build-core", ref="main")
     ),
-    Project(repo=Repository(owner="sphinx-doc", name="sphinx", ref="master")),
+    Project(
+        repo=Repository(
+            owner="sphinx-doc",
+            name="sphinx",
+            ref="master",
+        ),
+        format_options=FormatOptions(
+            # Does not contain valid UTF-8
+            exclude="tests/roots/test-pycode/cp_1251_coded.py"
+        ),
+    ),
     Project(repo=Repository(owner="spruceid", name="siwe-py", ref="main")),
     Project(repo=Repository(owner="tiangolo", name="fastapi", ref="master")),
     Project(repo=Repository(owner="yandex", name="ch-backup", ref="main")),