diff --git a/pkgs/development/ocaml-modules/x509/default.nix b/pkgs/development/ocaml-modules/x509/default.nix
index 91a478df8844..9bfe9489444c 100644
--- a/pkgs/development/ocaml-modules/x509/default.nix
+++ b/pkgs/development/ocaml-modules/x509/default.nix
@@ -10,9 +10,11 @@ buildDunePackage rec {
   pname = "x509";
   version = "0.16.2";
 
+  duneVersion = "3";
+
   src = fetchurl {
     url = "https://github.com/mirleft/ocaml-x509/releases/download/v${version}/x509-${version}.tbz";
-    sha256 = "sha256-Zf/ZZjUAkeWe04XLmqMKgbxN/qe/Z1mpKM82veXVf2I=";
+    hash = "sha256-Zf/ZZjUAkeWe04XLmqMKgbxN/qe/Z1mpKM82veXVf2I=";
   };
 
   nativeCheckInputs = [ alcotest cstruct-unix ];