diff --git a/ci-tools/update-grid-servers b/ci-tools/update-grid-servers
index 7d2debb38bfae7c888b4aa4d449f0a85f97bd6f5..51ebc6211bf42a48e0e0c7535ffc343f9c58617c 100755
--- a/ci-tools/update-grid-servers
+++ b/ci-tools/update-grid-servers
@@ -79,7 +79,7 @@ update_grid_nodes() {
     # Find the names of all hosts that belong to this grid.  This list includes
     # one extra string, "network", which is morph configuration stuff and we need
     # to filter out later.
-    nodes=$(nix --extra-experimental-features nix-command eval --impure --json "(builtins.concatStringsSep \" \" (builtins.attrNames (import $grid_dir/grid.nix)))" | jp --unquoted @)
+    nodes=$(nix --extra-experimental-features nix-command eval --impure --json --expr "(builtins.concatStringsSep \" \" (builtins.attrNames (import $grid_dir/grid.nix)))" | jp --unquoted @)
 
     # Tell every server in the network to update itself.
     for node in ${nodes}; do