diff --git a/ci-tools/update-nixpkgs b/ci-tools/update-nixpkgs
index 55c8ec67eb11382d0b22f8d87ec1ea85ba226c47..6fe5c16a4c5199ba5cdb775cc7fb348becf6ee6a 100755
--- a/ci-tools/update-nixpkgs
+++ b/ci-tools/update-nixpkgs
@@ -1,5 +1,5 @@
 #!/usr/bin/env nix-shell
-#!nix-shell -i sh -p nixUnstable git curl python3
+#!nix-shell -i sh -p nixUnstable git curl
 
 set -eux -o pipefail
 
@@ -10,7 +10,7 @@ nix-build -A morph -o result-before
 
 git checkout "${TARGET_BRANCH}" || git checkout -b "${TARGET_BRANCH}"
 
-./tools/update-nixpkgs
+nix-shell ./tools/ --run update-nixpkgs
 nix-build -A morph -o result-after
 diff=$(nix --extra-experimental-features nix-command store diff-closures ./result-before/ ./result-after/)