diff --git a/nix/default.nix b/nix/default.nix
index 0f380373a53fc10aba0829a34c6ae84732e4c7a6..5bd4d181773a37483950d211d9759ab67b7cff4b 100644
--- a/nix/default.nix
+++ b/nix/default.nix
@@ -13,6 +13,7 @@ let mydir = builtins.getEnv("PWD");
         "coq=8.13.0" "alt-ergo=2.2.0"
         "why3=1.4.0" "why3-coq=1.4.0"
         "menhir=20211012"
+        "easy-format=1.3.2"
       ];
     # only pure nix packages. See mk_deriv below for adding opam2nix packages
     mk_buildInputs = { nixPackages ? [] } :