diff --git a/src/gen_rules.ml b/src/gen_rules.ml
index 82c12406..d90d26c8 100644
--- a/src/gen_rules.ml
+++ b/src/gen_rules.ml
@@ -610,7 +610,7 @@ module Gen(P : Install_rules.Params) = struct
       Lib.DB.get_compile_info (Scope.libs scope) lib.name
         ~allow_overlaps:lib.buildable.allow_overlapping_dependencies
     in
-    let requires, real_requires =
+    let requires =
       SC.Libs.requires sctx compile_info
         ~dir ~has_dot_merlin:true
     in
@@ -795,7 +795,7 @@ module Gen(P : Install_rules.Params) = struct
       };
 
     Merlin.make ()
-      ~requires:real_requires
+      ~requires:(Lib.Compile.requires compile_info)
       ~flags
       ~preprocess:(Buildable.single_preprocess lib.buildable)
       ~libname:lib.name
@@ -823,7 +823,8 @@ module Gen(P : Install_rules.Params) = struct
         SC.Deps.interpret sctx exes.buildable.preprocessor_deps
           ~scope ~dir
       in
-      Preprocessing.pp_and_lint_modules sctx ~dir ~dep_kind:Required ~modules ~scope
+      Preprocessing.pp_and_lint_modules sctx ~dir ~dep_kind:Required ~modules
+        ~scope
         ~preprocess:exes.buildable.preprocess
         ~preprocessor_deps
         ~lint:exes.buildable.lint
@@ -880,7 +881,7 @@ module Gen(P : Install_rules.Params) = struct
         ~pps:(Jbuild.Preprocess_map.pps exes.buildable.preprocess)
         ~allow_overlaps:exes.buildable.allow_overlapping_dependencies
     in
-    let requires, real_requires =
+    let requires =
       SC.Libs.requires sctx ~dir
         ~has_dot_merlin:true
         compile_info
@@ -905,7 +906,7 @@ module Gen(P : Install_rules.Params) = struct
       ~js_of_ocaml:exes.buildable.js_of_ocaml;
 
     Merlin.make ()
-      ~requires:real_requires
+      ~requires:(Lib.Compile.requires compile_info)
       ~flags:(Ocaml_flags.common flags)
       ~preprocess:(Buildable.single_preprocess exes.buildable)
       ~objs_dirs:(Path.Set.singleton obj_dir)
diff --git a/src/inline_tests.ml b/src/inline_tests.ml
index ffb8473f..a4e75529 100644
--- a/src/inline_tests.ml
+++ b/src/inline_tests.ml
@@ -194,7 +194,7 @@ include Sub_system.Register_end_point(
         (Action.Var_expansion.Strings ([lib.name], Concat))
     in
 
-    let runner_libs, _ =
+    let runner_libs =
       let open Result.O in
       Lib.Compile.make
         (Result.concat_map backends
diff --git a/src/merlin.ml b/src/merlin.ml
index a3d10e39..0089079e 100644
--- a/src/merlin.ml
+++ b/src/merlin.ml
@@ -32,7 +32,7 @@ module Preprocess = struct
 end
 
 type t =
-  { requires   : (unit, Lib.t list) Build.t
+  { requires   : Lib.Set.t
   ; flags      : (unit, string list) Build.t
   ; preprocess : Preprocess.t
   ; libname    : string option
@@ -41,7 +41,7 @@ type t =
   }
 
 let make
-      ?(requires=Build.return [])
+      ?(requires=Ok [])
       ?(flags=Build.return [])
       ?(preprocess=Jbuild.Preprocess.No_preprocessing)
       ?libname
@@ -49,7 +49,12 @@ let make
       ?(objs_dirs=Path.Set.empty)
       () =
   (* Merlin shouldn't cause the build to fail, so we just ignore errors *)
-  { requires   = Build.catch requires ~on_error:(fun _ -> [])
+  let requires =
+    match requires with
+    | Ok    l -> Lib.Set.of_list l
+    | Error _ -> Lib.Set.empty
+  in
+  { requires
   ; flags      = Build.catch flags    ~on_error:(fun _ -> [])
   ; preprocess = Preprocess.make preprocess
   ; libname
@@ -92,11 +97,11 @@ let dot_merlin sctx ~dir ~scope ({ requires; flags; _ } as t) =
        >>>
        Build.create_file (Path.relative dir ".merlin-exists"));
     SC.add_rule sctx ~mode:Promote_but_delete_on_clean (
-      requires &&& flags
-      >>^ (fun (libs, flags) ->
+      flags
+      >>^ (fun flags ->
         let ppx_flags = ppx_flags sctx ~dir ~scope ~src_dir:remaindir t in
         let libs =
-          List.fold_left ~f:(fun acc (lib : Lib.t) ->
+          Lib.Set.fold requires ~init:[] ~f:(fun (lib : Lib.t) acc ->
             let serialize_path = Path.reach ~from:remaindir in
             let bpath = serialize_path (Lib.obj_dir lib) in
             let spath =
@@ -105,7 +110,7 @@ let dot_merlin sctx ~dir ~scope ({ requires; flags; _ } as t) =
               |> serialize_path
             in
             ("B " ^ bpath) :: ("S " ^ spath) :: acc
-          ) libs ~init:[]
+          )
         in
         let source_dirs =
           Path.Set.fold t.source_dirs ~init:[] ~f:(fun path acc ->
@@ -147,10 +152,7 @@ let dot_merlin sctx ~dir ~scope ({ requires; flags; _ } as t) =
     ()
 
 let merge_two a b =
-  { requires =
-      (Build.fanout a.requires b.requires
-       >>^ fun (x, y) ->
-       Lib.L.remove_dups (x @ y))
+  { requires = Lib.Set.union a.requires b.requires
   ; flags = a.flags &&& b.flags >>^ (fun (a, b) -> a @ b)
   ; preprocess = Preprocess.merge a.preprocess b.preprocess
   ; libname =
diff --git a/src/merlin.mli b/src/merlin.mli
index 9b552e26..1963cd93 100644
--- a/src/merlin.mli
+++ b/src/merlin.mli
@@ -1,9 +1,11 @@
 (** Merlin rules *)
 
+open Import
+
 type t
 
 val make
-  :  ?requires:(unit, Lib.t list) Build.t
+  :  ?requires:(Lib.t list, exn) result
   -> ?flags:(unit, string list) Build.t
   -> ?preprocess:Jbuild.Preprocess.t
   -> ?libname:string
diff --git a/src/super_context.ml b/src/super_context.ml
index 1e31c7bb..752dae76 100644
--- a/src/super_context.ml
+++ b/src/super_context.ml
@@ -284,15 +284,12 @@ module Libs = struct
                  Required)
       >>> requires
     in
-    let requires_with_merlin =
-      if t.context.merlin && has_dot_merlin then
-        Build.path (Path.relative dir ".merlin-exists")
-        >>>
-        requires
-      else
-        requires
-    in
-    (requires_with_merlin, requires)
+    if t.context.merlin && has_dot_merlin then
+      Build.path (Path.relative dir ".merlin-exists")
+      >>>
+      requires
+    else
+      requires
 
   let lib_files_alias ~dir ~name ~ext =
     Alias.make (sprintf "lib-%s%s-all" name ext) ~dir
diff --git a/src/super_context.mli b/src/super_context.mli
index dd6ded0f..5430a667 100644
--- a/src/super_context.mli
+++ b/src/super_context.mli
@@ -131,15 +131,13 @@ val resolve_program
 
 module Libs : sig
   (** Returns the closed list of dependencies for a dependency list in
-      a stanza. The second arrow is the same as the first one but with
-      an added dependency on the [.merlin] if [(context t).merlin &&
-      has_dot_merlin] is [true]. *)
+      a stanza. *)
   val requires
     :  t
     -> dir:Path.t
     -> has_dot_merlin:bool
     -> Lib.Compile.t
-    -> (unit, Lib.L.t) Build.t * (unit, Lib.L.t) Build.t
+    -> (unit, Lib.L.t) Build.t
 
   (** [file_deps ~ext] is an arrow that record dependencies on all the
       files with extension [ext] of the libraries given as input. *)
diff --git a/src/utop.ml b/src/utop.ml
index 99ba693a..e39f3193 100644
--- a/src/utop.ml
+++ b/src/utop.ml
@@ -62,7 +62,7 @@ let setup sctx ~dir ~(libs : Library.t list) ~scope =
         ; intf = None
         ; obj_name = "" } in
     let utop_exe_dir = utop_exe_dir ~dir in
-    let requires, _ =
+    let requires =
       Lib.DB.find_many (Scope.libs scope)
         ("utop" :: List.map libs ~f:(fun (lib : Library.t) -> lib.name))
       |> Lib.Compile.make