diff --git a/pkgs/development/tools/ocaml/ocp-index/default.nix b/pkgs/development/tools/ocaml/ocp-index/default.nix
index 6c315960f985..5b37febbb998 100644
--- a/pkgs/development/tools/ocaml/ocp-index/default.nix
+++ b/pkgs/development/tools/ocaml/ocp-index/default.nix
@@ -4,6 +4,8 @@ buildDunePackage rec {
   pname = "ocp-index";
   version = "1.3.4";
 
+  duneVersion = "3";
+
   minimalOCamlVersion = "4.08";
 
   src = fetchFromGitHub {