diff --git a/src/stdune/univ_map.ml b/src/stdune/univ_map.ml
index fcb2fb64..9bdb0f20 100644
--- a/src/stdune/univ_map.ml
+++ b/src/stdune/univ_map.ml
@@ -71,3 +71,4 @@ let find_exn t key =
     let eq = Key.eq key' key in
     Eq.cast eq v
 
+let singleton key v = Int.Map.singleton (Key.id key) (Binding.T (key, v))
diff --git a/src/stdune/univ_map.mli b/src/stdune/univ_map.mli
index 5c9b76eb..6cea4955 100644
--- a/src/stdune/univ_map.mli
+++ b/src/stdune/univ_map.mli
@@ -17,3 +17,4 @@ val add      : t -> 'a Key.t -> 'a -> t
 val remove   : t -> 'a Key.t -> t
 val find     : t -> 'a Key.t -> 'a option
 val find_exn : t -> 'a Key.t -> 'a
+val singleton : 'a Key.t -> 'a -> t