diff --git a/pkgs/development/ocaml-modules/mec/default.nix b/pkgs/development/ocaml-modules/mec/default.nix
index 8381cf821ed3..9811c502596d 100644
--- a/pkgs/development/ocaml-modules/mec/default.nix
+++ b/pkgs/development/ocaml-modules/mec/default.nix
@@ -10,6 +10,8 @@ buildDunePackage rec {
     sha256 = "sha256-uIcGj/exSfuuzsv6C/bnJXpYRu3OY3dcKMW/7+qwi2U=";
   };
 
+  duneVersion = "3";
+
   minimalOCamlVersion = "4.12";
 
   propagatedBuildInputs = [