diff --git a/nix/Dockerfile b/nix/Dockerfile
index 935f0d7..615178a 100644
--- a/nix/Dockerfile
+++ b/nix/Dockerfile
@@ -1,4 +1,5 @@
 FROM nixos/nix:2.25.3
-RUN echo "nixpkgs.config.allowUnfree = true" >> /etc/nix/nix.conf
+
+ENV NIXPKGS_ALLOW_UNFREE=1
 # enable nix-command and flakes
 RUN echo "experimental-features = nix-command flakes" >> /etc/nix/nix.conf