diff --git a/bin/main.ml b/bin/main.ml
index a7565d7b..a4db00ff 100644
--- a/bin/main.ml
+++ b/bin/main.ml
@@ -111,7 +111,7 @@ let build_package =
 let external_lib_deps packages =
   let log = create_log () in
   let deps =
-    Path.Map.fold (Main.external_lib_deps ~log ~packages) ~init:String_map.empty
+    Path.Map.fold (Main.external_lib_deps ~log ~packages ()) ~init:String_map.empty
       ~f:(fun ~key:_ ~data:deps acc -> Build.merge_lib_deps deps acc)
   in
   String_map.iter deps ~f:(fun ~key:n ~data ->
diff --git a/src/main.ml b/src/main.ml
index 0fc23cfd..36a240a8 100644
--- a/src/main.ml
+++ b/src/main.ml
@@ -27,7 +27,7 @@ let setup ?filter_out_optional_stanzas_with_missing_deps () =
          ; packages
          }
 
-let external_lib_deps ?log ~packages =
+let external_lib_deps ?log ~packages () =
   Future.Scheduler.go ?log
     (setup () ~filter_out_optional_stanzas_with_missing_deps:false
      >>| fun ({ build_system = bs; stanzas; _ } as setup) ->
diff --git a/src/main.mli b/src/main.mli
index fe21116e..544272f3 100644
--- a/src/main.mli
+++ b/src/main.mli
@@ -17,6 +17,7 @@ val setup
 val external_lib_deps
   : ?log:out_channel
   -> packages:string list
+  -> unit
   -> Build.lib_deps Path.Map.t
 val report_error : ?map_fname:(string -> string) -> Format.formatter -> exn -> unit