diff --git a/www/nginx/src/opnsense/service/templates/OPNsense/Nginx/security_rule.conf b/www/nginx/src/opnsense/service/templates/OPNsense/Nginx/security_rule.conf
index 354db6121..73ab27993 100644
--- a/www/nginx/src/opnsense/service/templates/OPNsense/Nginx/security_rule.conf
+++ b/www/nginx/src/opnsense/service/templates/OPNsense/Nginx/security_rule.conf
@@ -12,7 +12,7 @@
 {% endif %}
 {% if security_rule.strict_transport_security_time is defined %}
 {% do our_headers.append('Strict-Transport-Security') %}
-    add_header Strict-Transport-Security "{{ security_rule.strict_transport_security_time }}{%
+    add_header Strict-Transport-Security "max-age={{ security_rule.strict_transport_security_time }}{%
   if security_rule.strict_transport_security_include_subdomains is defined and
      security_rule.strict_transport_security_include_subdomains == '1' %}; includeSubDomains{% endif %}" always;
 {% endif %}