diff --git a/ci-tools/update-nixpkgs b/ci-tools/update-nixpkgs
index 2c055fdfc4d71b32267b57f1b239909c236b57b3..f30bc254e558e3149c230d1fe6be49c45ab693e4 100755
--- a/ci-tools/update-nixpkgs
+++ b/ci-tools/update-nixpkgs
@@ -39,7 +39,7 @@ git checkout "${TARGET_BRANCH}" || git checkout -b "${TARGET_BRANCH}"
 
 # Spawn *another* nix-shell that has the *other* update-nixpkgs tool.  Should
 # sort out this mess sooner rather than later...
-nix-shell ./shell.nix --run update-nixpkgs
+nix-shell ./shell.nix --run 'update-nixpkgs --dry-run'
 
 # Show us what we did
 if git diff --exit-code; then