diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 0211783ab95083ffba0bec80de1a4956f702fdbb..1706beda3156d229a453415d26d8119ba6487a38 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -7,6 +7,7 @@ variables:
     DEFAULT: "master"
     OCAML: "4_08"
     FRAMA_CI_OPT: "--override frama-clang:$CI_COMMIT_REF_NAME,$CI_COMMIT_SHA"
+    NIXPKGS_ALLOW_UNFREE: "1"
 
 #avoid a nix error https://github.com/NixOS/nix/issues/2087
 git-update: