diff --git a/lsp/src/uri0.ml b/lsp/src/uri0.ml
index 6391189c6..605bc10f1 100644
--- a/lsp/src/uri0.ml
+++ b/lsp/src/uri0.ml
@@ -1,5 +1,9 @@
 open Import
 
+module Private = struct
+  let win32 = ref Sys.win32
+end
+
 type t = Uri_lexer.t =
   { scheme : string option
   ; authority : string
@@ -46,7 +50,7 @@ let to_path t =
     |> String.replace_all ~pattern:"%3D" ~with_:"="
     |> String.replace_all ~pattern:"%3F" ~with_:"?"
   in
-  if Sys.win32 then path else Filename.concat "/" path
+  if !Private.win32 then path else Filename.concat "/" path
 
 let of_path (path : string) =
   let path = Uri_lexer.escape_path path in
diff --git a/lsp/src/uri0.mli b/lsp/src/uri0.mli
index b28ea36d9..d186e85b0 100644
--- a/lsp/src/uri0.mli
+++ b/lsp/src/uri0.mli
@@ -17,3 +17,7 @@ val to_path : t -> string
 val of_path : string -> t
 
 val to_string : t -> string
+
+module Private : sig
+  val win32 : bool ref
+end
diff --git a/lsp/test/uri_tests.ml b/lsp/test/uri_tests.ml
index ed1467bf8..c18a0ec2a 100644
--- a/lsp/test/uri_tests.ml
+++ b/lsp/test/uri_tests.ml
@@ -1,25 +1,43 @@
 open Lsp
 
+let run_with_modes f =
+  print_endline "Unix:";
+  Lsp.Uri.Private.win32 := false;
+  f ();
+  print_endline "Windows:";
+  Lsp.Uri.Private.win32 := true;
+  f ()
+
+let test_uri_parsing =
+  let test s =
+    let uri = Uri.t_of_yojson (`String s) in
+    Printf.printf "%s -> %s\n" s (Uri.to_path uri)
+  in
+  fun uris -> run_with_modes (fun () -> List.iter test uris)
+
 let%expect_test "test uri parsing" =
-  let uri = Uri.t_of_yojson (`String "file:///Users/foo") in
-  print_endline (Uri.to_path uri);
-  [%expect {|
-    /Users/foo |}];
-  print_endline (Uri.to_string uri);
-  [%expect {| file:///Users/foo |}];
-  let uri = Uri.t_of_yojson (`String "file:///c:/Users/foo") in
-  print_endline (Uri.to_path uri);
-  [%expect {| /c:/Users/foo |}];
-  print_endline (Uri.to_string uri);
+  test_uri_parsing [ "file:///Users/foo"; "file:///c:/Users/foo" ];
   [%expect {|
-    file:///c:/Users/foo |}]
+    Unix:
+    file:///Users/foo -> /Users/foo
+    file:///c:/Users/foo -> /c:/Users/foo
+    Windows:
+    file:///Users/foo -> Users/foo
+    file:///c:/Users/foo -> c:/Users/foo |}]
+
+let uri_of_path =
+  let test path =
+    let uri = Uri.of_path path in
+    Printf.printf "%s -> %s\n" path (Uri.to_string uri)
+  in
+  fun uris -> run_with_modes (fun () -> List.iter test uris)
 
 let%expect_test "uri of path" =
-  let uri = Uri.of_path "/foo/bar.ml" in
-  print_endline (Uri.to_string uri);
-  [%expect {|
-    file:///foo/bar.ml |}];
-  let uri = Uri.of_path "foo/bar.mli" in
-  print_endline (Uri.to_string uri);
+  uri_of_path [ "/foo/bar.ml"; "foo/bar.mli" ];
   [%expect {|
-    file:///foo/bar.mli |}]
+    Unix:
+    /foo/bar.ml -> file:///foo/bar.ml
+    foo/bar.mli -> file:///foo/bar.mli
+    Windows:
+    /foo/bar.ml -> file:///foo/bar.ml
+    foo/bar.mli -> file:///foo/bar.mli |}]