diff --git a/src/infra/nginx.conf b/src/infra/nginx.conf
index 2a4875e..d90c9f6 100644
--- a/src/infra/nginx.conf
+++ b/src/infra/nginx.conf
@@ -22,7 +22,9 @@ server {
     resolver_timeout 5s;
     set $backend_url ${API_BACKEND_URL};
     proxy_pass http://$backend_url;
-    proxy_set_header Host $host;
+    # Use the backend hostname, not the incoming request's Host.
+    # Prevents routing loops when an ALB uses Host-based routing.
+    proxy_set_header Host $backend_url;
     proxy_set_header X-Real-IP $remote_addr;
     proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
     proxy_set_header X-Forwarded-Proto $scheme;