diff --git a/src/util/shuffle.mli b/src/util/shuffle.mli
index 8de61a2ecd8f243de16da1529276b768b26523ab..71eb1e3f467eab969fea24ae354843dcb82aab70 100644
--- a/src/util/shuffle.mli
+++ b/src/util/shuffle.mli
@@ -1,4 +1,3 @@
-
 val set_shuffle: int array option -> unit
 (** if None is given shuffling is disable (default) *)
 
@@ -23,5 +22,8 @@ val seql': ('a -> unit) -> 'a list -> unit
 val seql : (unit -> unit) list -> unit
 
 val chooseb: ('a -> 'b) -> ((unit -> bool) ->'a -> 'b) -> 'a -> 'b
+(** [chooseb f g] call f if there is no shuffling or g otherwise.
+    The first argument given to g is a random boolean generator.
+*)
 
 val int: int -> int