diff --git a/pkgs/development/ocaml-modules/iter/default.nix b/pkgs/development/ocaml-modules/iter/default.nix
index 26adaf06d1ee..7d0f9366a554 100644
--- a/pkgs/development/ocaml-modules/iter/default.nix
+++ b/pkgs/development/ocaml-modules/iter/default.nix
@@ -7,6 +7,8 @@ buildDunePackage rec {
   pname = "iter";
   version = "1.6";
 
+  duneVersion = "3";
+
   src = fetchFromGitHub {
     owner = "c-cube";
     repo = pname;