diff --git a/nix/default.nix b/nix/default.nix
index 750fa89523c53ed6596ef04334e67d28a3db6a4f..2c8fdf94fbf13ca256470e73f6f3fa08b581b07f 100644
--- a/nix/default.nix
+++ b/nix/default.nix
@@ -20,7 +20,7 @@ let frama_clang_build =
    { inherit pkgs stdenv src opam2nix ocaml_version plugins;
      name = "frama-clang-on-llvm-" + llvm_version;
      deps = [ llvm_package.clang-unwrapped llvm pkgs.gnused ];
-     opamPackages = [ "camlp5" ];
+     opamPackages = [ { name = "camlp5"; constraint="=7.14";} ];
      preFramaCTests = ''
        echo CONFIGURING Why3 for Frama_Clang.
        export HOME=$(mktemp -d)
diff --git a/nix/frama-ci.nix b/nix/frama-ci.nix
index 700557f26620b2ea3212c86d5a03be17e2b2cc63..e2fc225275ac35df0a0887094f8ab1fc980d30d1 100644
--- a/nix/frama-ci.nix
+++ b/nix/frama-ci.nix
@@ -5,8 +5,8 @@ let
     src = builtins.fetchGit {
             "url" = "https://bobot:${password}@git.frama-c.com/frama-c/Frama-CI.git";
             "name" = "Frama-CI";
-            "rev" = "ec1a17f66dd629480beed8daeab4ececc5f0dc75";
-            "ref" = "master";
+            "rev" = "614b8c3f2be697384626581d84836d7a41dc6c38";
+            "ref" = "feature/headers/2021";
     };
  in
  {