diff --git a/setup.py b/setup.py
index def3417845d..1a8c03eb337 100644
--- a/setup.py
+++ b/setup.py
@@ -1001,7 +1001,7 @@ def debug_build() -> bool:
     return hasattr(sys, "gettotalrefcount") or FUZZING_BUILD
 
 
-files = ["src/_imaging.c"]
+files: list[str | os.PathLike[str]] = ["src/_imaging.c"]
 for src_file in _IMAGING:
     files.append("src/" + src_file + ".c")
 for src_file in _LIB_IMAGING: