diff --git a/internal/builder/builder.go b/internal/builder/builder.go
index 1bc99d9..ecafc96 100644
--- a/internal/builder/builder.go
+++ b/internal/builder/builder.go
@@ -1271,8 +1271,9 @@ func bundled(ctx context.Context, run Runner, tree string, chain Toolchain, base
 		launch = append(launch, out+"/"+l)
 	}
 	// Refused by name in an image that predates the bundler, as the dependencies copy is: a bundle
-	// packed without it would carry nothing it imports.
-	guard := `test -x "$0" || { echo "the toolchain image carries no bundler at $0: it predates one-file bundles, rebuild mesh-tools first" >&2; exit 1; }; exec node "$0" "$@"`
+	// packed without it would carry nothing it imports. Run as itself: npm installs esbuild's native
+	// binary in place of its script, which `node` cannot run.
+	guard := `test -x "$0" || { echo "the toolchain image carries no bundler at $0: it predates one-file bundles, rebuild mesh-tools first" >&2; exit 1; }; exec "$0" "$@"`
 	step := func(entries []string, extra ...string) error {
 		if len(entries) == 0 {
 			return nil