diff --git a/trovedb/fs_util.py b/trovedb/fs_util.py
index 2654be7..83dd673 100644
--- a/trovedb/fs_util.py
+++ b/trovedb/fs_util.py
@@ -90,8 +90,8 @@ def get_content_index_name_from_path(path: Path) -> str:
     """Return the name of the index file for a directory."""
     # TODO: improve handling and mimetype logic
     if not path.suffix:
-        return '_index.dat'
-    return f'_index{path.suffix}'
+        return 'index.dat'
+    return f'index{path.suffix}'
 
 def get_content_path(path: str | Path) -> Path:
     """Return the path to the content file for a directory or file"""