diff --git a/.drone.yml b/.drone.yml
index e051fde..400a326 100644
--- a/.drone.yml
+++ b/.drone.yml
@@ -7,6 +7,7 @@ steps:
   - name: build book docker image
     image: "monacoremo/nix:2020-04-05-05f09348-circleci"
     commands:
+      - echo '{ allowUnfree = true; }' > ~/.config/nixpkgs/config.nix
       - cd book && nix-build
       - cp $(readlink result) /lewa/result/docker.tgz
     volumes: