diff --git a/backend/routers/gateway_proxy.py b/backend/routers/gateway_proxy.py
index e75a807..0e25ccb 100644
--- a/backend/routers/gateway_proxy.py
+++ b/backend/routers/gateway_proxy.py
@@ -108,7 +108,8 @@ async def _proxy(path: str, request: Request):
     if vision_alias and alias not in VISION_CAPABLE and has_image(body):
         alias = vision_alias
         body["model"] = alias
-        routed = {"x-mc-routed-to": alias, "x-mc-route-reason": "Bild erkannt → Vision-Modell",
+        # HTTP-Header-Werte muessen latin-1 sein — kein '→' o.ae. (sonst 500, 13.07.).
+        routed = {"x-mc-routed-to": alias, "x-mc-route-reason": "Bild erkannt -> Vision-Modell",
                   "x-mc-lane": routed.get("x-mc-lane", "-")}
     # fast-Spur: Thinking aus für flotte Antworten (sofern Client es nicht selbst setzt).
     if pol["fast_no_think"] and alias == pol["fast"] and "chat_template_kwargs" not in body: