diff --git a/ci-tools/update-nixpkgs b/ci-tools/update-nixpkgs
index 6fe5c16a4c5199ba5cdb775cc7fb348becf6ee6a..fa0791ffab1f5c51cb0c2ce6c6ad25d2c806acb9 100755
--- a/ci-tools/update-nixpkgs
+++ b/ci-tools/update-nixpkgs
@@ -10,7 +10,10 @@ nix-build -A morph -o result-before
 
 git checkout "${TARGET_BRANCH}" || git checkout -b "${TARGET_BRANCH}"
 
-nix-shell ./tools/ --run update-nixpkgs
+# 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-build -A morph -o result-after
 diff=$(nix --extra-experimental-features nix-command store diff-closures ./result-before/ ./result-after/)