diff --git a/_oasis b/_oasis
index 3b4093d6..7c00af27 100644
--- a/_oasis
+++ b/_oasis
@@ -201,7 +201,7 @@ Executable run_qtest
   Install:          false
   CompiledObject:   best
   MainIs:           run_qtest.ml
-  Build$:           flag(tests) && flag(bigarray) && flag(unix)
+  Build$:           flag(tests) && flag(bigarray) && flag(unix) && flag(advanced)
   BuildDepends:     containers, containers.misc, containers.string, containers.iter,
                     containers.io, containers.advanced, containers.sexp,
                     containers.bigarray, containers.unix,
diff --git a/benchs/run_benchs.ml b/benchs/run_benchs.ml
index 5fa29837..257b092c 100644
--- a/benchs/run_benchs.ml
+++ b/benchs/run_benchs.ml
@@ -4,6 +4,7 @@ module B = Benchmark
 let (@>) = B.Tree.(@>)
 let (@>>) = B.Tree.(@>>)
 let (@>>>) = B.Tree.(@>>>)
+let (|>) = CCFun.(|>)
 
 let app_int f n = string_of_int n @> lazy (f n)
 let app_ints f l = B.Tree.concat (List.map (app_int f) l)
diff --git a/src/lwt/lwt_pipe.mli b/src/lwt/lwt_pipe.mli
index 46702c78..fce6de12 100644
--- a/src/lwt/lwt_pipe.mli
+++ b/src/lwt/lwt_pipe.mli
@@ -74,20 +74,20 @@ type ('a, +'perm) t constraint 'perm = [< `r | `w]
 
 type ('a, 'perm) pipe = ('a, 'perm) t
 
-val keep : _ t -> unit Lwt.t -> unit
+val keep : (_,_) t -> unit Lwt.t -> unit
 (** [keep p fut] adds a pointer from [p] to [fut] so that [fut] is not
     garbage-collected before [p] *)
 
-val is_closed : _ t -> bool
+val is_closed : (_,_) t -> bool
 
-val close : _ t -> unit Lwt.t
+val close : (_,_) t -> unit Lwt.t
 (** [close p] closes [p], which will not accept input anymore.
     This sends [`End] to all readers connected to [p] *)
 
-val close_async : _ t -> unit
+val close_async : (_,_) t -> unit
 (** Same as {!close} but closes in the background *)
 
-val wait : _ t -> unit Lwt.t
+val wait : (_,_) t -> unit Lwt.t
 (** Evaluates once the pipe closes *)
 
 val create : ?max_size:int -> unit -> ('a, 'perm) t
@@ -101,7 +101,7 @@ val connect : ?ownership:[`None | `InOwnsOut | `OutOwnsIn] ->
     @param own determines which pipes owns which (the owner, when it
       closes, also closes the ownee) *)
 
-val link_close : _ t -> after:_ t -> unit
+val link_close : (_,_) t -> after:(_,_) t -> unit
 (** [link_close p ~after] will close [p] when [after] closes.
     if [after] is closed already, closes [p] immediately *)
 
diff --git a/src/misc/backtrack.ml b/src/misc/backtrack.ml
index ccb25a85..db0d06d9 100644
--- a/src/misc/backtrack.ml
+++ b/src/misc/backtrack.ml
@@ -88,6 +88,7 @@ module Logical (P:Param) = struct
     | Zero e -> f e
     | Plus (a1, f1) ->
       plus a1 (fun e -> plus (f1 e) f)
+    | _ -> Plus (a, f)
 
   let split x = Split x