diff --git a/pkgs/development/ocaml-modules/fiber/default.nix b/pkgs/development/ocaml-modules/fiber/default.nix
index fe805c82a35..da5e4580e16 100644
--- a/pkgs/development/ocaml-modules/fiber/default.nix
+++ b/pkgs/development/ocaml-modules/fiber/default.nix
@@ -1,22 +1,23 @@
-{ lib, buildDunePackage, dune_3, stdune, dyn }:
+{ lib, buildDunePackage, fetchFromGitHub, stdune, dyn }:
 
 buildDunePackage rec {
   pname = "fiber";
-  inherit (dune_3) src version;
+  version = "unstable-2023-02-28";
+
+  src = fetchFromGitHub {
+    owner = "ocaml-dune";
+    repo = "fiber";
+    rev = "5563b588c1313f128eafa74d66f0626c9128d34d";
+    hash = "sha256-18GfGXpu+uiIiCuLhIx5z5jRkem1nNWaQB6Ms0AE9sE=";
+  };
 
   duneVersion = "3";
 
-  dontAddPrefix = true;
-
   buildInputs = [ stdune dyn ];
 
-  preBuild = ''
-    rm -r vendor/csexp
-  '';
-
   meta = with lib; {
     description = "Structured concurrency library";
-    inherit (dune_3.meta) homepage;
+    homepage = "https://github.com/ocaml-dune/fiber";
     maintainers = with lib.maintainers; [ ];
     license = licenses.mit;
   };