diff --git a/src/Sequence.ml b/src/Sequence.ml
index af94eb8..47b8f70 100644
--- a/src/Sequence.ml
+++ b/src/Sequence.ml
@@ -407,7 +407,10 @@ let group_succ_by ?(eq=fun x y -> x = y) seq k =
         k l; (* yield group, and start another one *)
         cur := [x]);
   (* last list *)
-  if !cur <> [] then k !cur
+  begin match !cur with
+    | [] -> ()
+    | (_::_) as l -> k l
+  end
 
 (*$R
   [1;2;3;3;2;2;3;4]
diff --git a/src/Sequence.mli b/src/Sequence.mli
index c7b19a2..8e1d525 100644
--- a/src/Sequence.mli
+++ b/src/Sequence.mli
@@ -261,7 +261,7 @@ val sorted : ?cmp:('a -> 'a -> int) -> 'a t -> bool
     @since 0.9 *)
 
 val group_succ_by : ?eq:('a -> 'a -> bool) -> 'a t -> 'a list t
-(** Group equal consecutive elements.
+(** Group equal consecutive elements. Linear time.
     Formerly synonym to [group].
     @since 0.6 *)