diff --git a/bootstrap.sh b/bootstrap.sh
index af9e050..2f5bac9 100755
--- a/bootstrap.sh
+++ b/bootstrap.sh
@@ -48,7 +48,7 @@ echo ""
 
 # ── Option 3: already running from inside the repo ───────────────────────────
 # If setup.sh is sitting next to this script, we have everything we need.
-SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" 2>/dev/null && pwd || echo "")"
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]:-}")" 2>/dev/null && pwd || echo "")"
 if [ -f "${SCRIPT_DIR}/setup.sh" ]; then
     echo "  Running from local copy at $SCRIPT_DIR"
     echo "  (No git or internet needed)"