diff --git a/routes/waterfall_websocket.py b/routes/waterfall_websocket.py
index 15d14c9..260c044 100644
--- a/routes/waterfall_websocket.py
+++ b/routes/waterfall_websocket.py
@@ -1,5 +1,7 @@
 """WebSocket-based waterfall streaming with I/Q capture and server-side FFT."""
 
+from __future__ import annotations
+
 import json
 import queue
 import socket