diff --git a/src/data/CCImmutArray.mli b/src/data/CCImmutArray.mli
index 3bb7c4d5..f74d7d43 100644
--- a/src/data/CCImmutArray.mli
+++ b/src/data/CCImmutArray.mli
@@ -37,9 +37,13 @@ val set : 'a t -> int -> 'a -> 'a t
 (** Copy the array and modify its copy *)
 
 val sub : 'a t -> int -> int -> 'a t
-(** [sub a start len] returns a fresh array of length len, containing the elements number start to start + len - 1 of array a.
-    Raises [Invalid_argument "Array.sub"] if start and len do not designate a valid subarray of a; that is, if start < 0, or len < 0, or start + len > Array.length a. *)
- 
+(** [sub a start len] returns a fresh array of length len, containing the elements
+    from [start] to pstart + len - 1] of array a.
+
+    Raises [Invalid_argument "Array.sub"] if [start] and [len] do not designate a
+    valid subarray of a; that is, if start < 0, or len < 0, or start + len > Array.length a.
+
+    @since NEXT_RELEASE *)
 
 val map : ('a -> 'b) -> 'a t -> 'b t