diff --git a/src/data/CCWBTree.ml b/src/data/CCWBTree.ml
index fe4cd5f5..8b395062 100644
--- a/src/data/CCWBTree.ml
+++ b/src/data/CCWBTree.ml
@@ -25,6 +25,8 @@ module type S = sig
 
   val empty : 'a t
 
+  val is_empty : _ t -> bool
+
   val mem : key -> _ t -> bool
 
   val get : key -> 'a t -> 'a option
@@ -97,6 +99,10 @@ module MakeFull(K : KEY) : S with type key = K.t = struct
 
   let empty = E
 
+  let is_empty = function
+    | E -> true
+    | N _ -> false
+
   let rec get_exn k m = match m with
     | E -> raise Not_found
     | N (k', v, l, r, _) ->
diff --git a/src/data/CCWBTree.mli b/src/data/CCWBTree.mli
index 87eb975e..f74c27b0 100644
--- a/src/data/CCWBTree.mli
+++ b/src/data/CCWBTree.mli
@@ -30,6 +30,8 @@ module type S = sig
 
   val empty : 'a t
 
+  val is_empty : _ t -> bool
+
   val mem : key -> _ t -> bool
 
   val get : key -> 'a t -> 'a option