diff --git a/src/index-format/index_format.ml b/src/index-format/index_format.ml
index 26978d029..e85560b16 100644
--- a/src/index-format/index_format.ml
+++ b/src/index-format/index_format.ml
@@ -31,6 +31,7 @@ type index = {
   approximated : Lid_set.t Uid_map.t;
   cu_shape : (string, Shape.t) Hashtbl.t;
   stats : stat Stats.t;
+  root_directory: string option;
 }
 
 let pp_partials (fmt : Format.formatter) (partials : Lid_set.t Uid_map.t) =
diff --git a/src/index-format/index_format.mli b/src/index-format/index_format.mli
index 3b3866eb6..822acbae1 100644
--- a/src/index-format/index_format.mli
+++ b/src/index-format/index_format.mli
@@ -19,6 +19,7 @@ type index = {
   approximated : Lid_set.t Uid_map.t;
   cu_shape : (string, Shape.t) Hashtbl.t;
   stats : stat Stats.t;
+  root_directory: string option;
 }
 
 val pp : Format.formatter -> index -> unit