diff --git a/nix/default.nix b/nix/default.nix
index ba25519912fa66efcfd5e7d4029a62aed9bf3a3d..7d5b49d4dfa1f65a0c7064a79a2220fda842ee90 100644
--- a/nix/default.nix
+++ b/nix/default.nix
@@ -14,6 +14,7 @@ let mydir = builtins.getEnv("PWD");
         "why3=1.5.0" "why3-coq=1.5.0"
         "menhir=20211012"
         "easy-format=1.3.2"
+        "biniou=1.2.1"
       ];
     # only pure nix packages. See mk_deriv below for adding opam2nix packages
     mk_buildInputs = { nixPackages ? [] } :