diff --git a/nixos/modules/update-deployment b/nixos/modules/update-deployment
index 9bc82489acaedc59ed238a8ff756762b6616a4ff..cd41a2363c699c7e551a33d73f1eb83996c1ca85 100755
--- a/nixos/modules/update-deployment
+++ b/nixos/modules/update-deployment
@@ -82,7 +82,7 @@ ssh -o StrictHostKeyChecking=no "$(hostname).$(domainname)" ":"
 
 # Two lines since 'export' masks 'set -e'
 # See https://mywiki.wooledge.org/BashFAQ/105#line-204
-NIX_PATH="nixpkgs=$(nix eval "(import ${CHECKOUT}/nixpkgs.nix { }).path")"
+NIX_PATH="nixpkgs=$(nix --extra-experimental-features nix-command eval --impure --expr "(import ${CHECKOUT}/nixpkgs.nix { }).path")"
 export NIX_PATH
 
 # Attempt to update just this host.  Choose the morph grid definition matching