diff --git a/src/sphinx_autodoc_typehints/__init__.py b/src/sphinx_autodoc_typehints/__init__.py
index 8ea71c4..e67180f 100644
--- a/src/sphinx_autodoc_typehints/__init__.py
+++ b/src/sphinx_autodoc_typehints/__init__.py
@@ -356,7 +356,7 @@ def process_signature(  # noqa: C901, PLR0913, PLR0917
     sph_signature = sphinx_signature(obj, type_aliases=app.config["autodoc_type_aliases"])
     typehints_formatter: Callable[..., str | None] | None = getattr(app.config, "typehints_formatter", None)
 
-    def _get_formatted_annotation(annotation):
+    def _get_formatted_annotation(annotation: TypeVar) -> TypeVar:
         if typehints_formatter is None:
             return annotation
         formatted_name = typehints_formatter(annotation)
diff --git a/tests/test_integration.py b/tests/test_integration.py
index 9fe8ac6..93aa1e5 100644
--- a/tests/test_integration.py
+++ b/tests/test_integration.py
@@ -1406,7 +1406,7 @@ def has_doctest1() -> None:
     """,
     typehints_use_signature=True,
     typehints_use_signature_return=True,
-    typehints_formatter=lambda ann, cfg=None: "Formatted",
+    typehints_formatter=lambda _, __=None: "Formatted",
 )
 def typehints_formatter_applied_to_signature(param: Unformatted) -> Unformatted:
     """