diff --git a/CHANGES.md b/CHANGES.md
index 998b1659a21..e2a97a4c98e 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -92,6 +92,10 @@
   relies on the version written in the `dune-project` file and no
   longer read `VERSION` or similar files (#2541, @diml)
 
+- On Windows, an .exe suffix is no longer added implicitly to binary names that
+  already end in .exe. Second, when resolving binary names, .opt variants are no
+  longer chosen automatically. (#2543, @nojb)
+
 1.11.0 (23/07/2019)
 -------------------
 
diff --git a/src/dune/context.ml b/src/dune/context.ml
index 157555151b7..03369df0d74 100644
--- a/src/dune/context.ml
+++ b/src/dune/context.ml
@@ -151,7 +151,20 @@ let opam_config_var ~env ~cache var =
         | Error _ ->
             None ) )
 
-let which ~cache ~path x = Table.find_or_add cache x ~f:(Bin.which ~path)
+let best_prog dir prog =
+  let fn = Path.relative dir (prog ^ ".opt" ^ Bin.exe) in
+  if Bin.exists fn then
+    Some fn
+  else
+    let fn = Path.relative dir (prog ^ Bin.exe) in
+    if Bin.exists fn then
+      Some fn
+    else
+      None
+
+let which ~path prog = List.find_map path ~f:(fun dir -> best_prog dir prog)
+
+let which ~cache ~path x = Table.find_or_add cache x ~f:(which ~path)
 
 let ocamlpath_sep =
   if Sys.cygwin then
@@ -273,7 +286,7 @@ let create ~(kind : Kind.t) ~path ~env ~env_nodes ~name ~merlin ~targets
     let get_ocaml_tool prog =
       match get_tool_using_findlib_config prog with
       | None ->
-          Bin.best_prog dir prog
+          best_prog dir prog
       | Some _ as x ->
           x
     in
diff --git a/src/stdune/bin.ml b/src/stdune/bin.ml
index b4f9ad2930d..df2eaf0fff9 100644
--- a/src/stdune/bin.ml
+++ b/src/stdune/bin.ml
@@ -31,25 +31,17 @@ let exists fn =
   | _ ->
       true
 
-let best_prog dir prog =
-  let fn = Path.relative dir (prog ^ ".opt" ^ exe) in
-  if exists fn then
-    Some fn
+let add_exe prog =
+  if String.is_suffix (String.lowercase prog) ~suffix:exe then
+    prog
   else
-    let fn = Path.relative dir (prog ^ exe) in
-    if exists fn then
-      Some fn
-    else
-      None
+    prog ^ exe
 
 let which ~path prog =
-  let rec search = function
-    | [] ->
-        None
-    | dir :: rest -> (
-      match best_prog dir prog with None -> search rest | Some fn -> Some fn )
-  in
-  search path
+  let prog = add_exe prog in
+  List.find_map path ~f:(fun dir ->
+      let fn = Path.relative dir prog in
+      Option.some_if (exists fn) fn)
 
 let make ~path =
   match which ~path "gmake" with None -> which ~path "make" | some -> some
diff --git a/src/stdune/bin.mli b/src/stdune/bin.mli
index dfab1048ea3..e0b93b55c9c 100644
--- a/src/stdune/bin.mli
+++ b/src/stdune/bin.mli
@@ -13,12 +13,11 @@ val cons_path : Path.t -> _PATH:string option -> string
 (** Extension to append to executable filenames *)
 val exe : string
 
+(** Check if a file exists *)
+val exists : Path.t -> bool
+
 (** Look for a program in the PATH *)
 val which : path:Path.t list -> string -> Path.t option
 
-(** Return the .opt version of a tool if available. If the tool is not
-    available at all in the given directory, returns [None]. *)
-val best_prog : Path.t -> string -> Path.t option
-
 (** "make" program *)
 val make : path:Path.t list -> Path.t option