diff --git a/backend/templates/_listen.conf b/backend/templates/_listen.conf
index 2b5973e51..50b1f1f3b 100644
--- a/backend/templates/_listen.conf
+++ b/backend/templates/_listen.conf
@@ -10,7 +10,10 @@
   listen 443 quic;
   listen [::]:443 quic;
 
-  add_header Alt-Svc 'h3=":443"; ma=86400';
+  more_set_headers "Alt-Svc: h3=':443'; ma=86400";
 {% endif %}
 {% endif %}
+{% unless hsts_subdomains %}
+  more_clear_headers "Alt-Svc";
+{% endunless %}
   server_name {{ domain_names | join: " " }};