diff --git a/fe/ac-fe-upstream.conf b/fe/ac-fe-upstream.conf
index ce1a540..424a73e 100644
--- a/fe/ac-fe-upstream.conf
+++ b/fe/ac-fe-upstream.conf
@@ -1,6 +1,11 @@
 # Shared cluster upstream — include in http {} before apps.conf / ac-fe.conf.
 # STAGING/DEV: cast01–03 lab cluster (no artc0).
 
+map $http_upgrade $connection_upgrade {
+	default upgrade;
+	''      close;
+}
+
 upstream ac_be_backend {
 	server cast01.intra.raptor.org:80;
 	server cast02.intra.raptor.org:80 backup;