diff --git a/source/_headers b/source/_headers
index c054842..c5c3865 100644
--- a/source/_headers
+++ b/source/_headers
@@ -4,7 +4,7 @@
   Expires: 0
   Feature-Policy: accelerometer 'none'; ambient-light-sensor 'none'; autoplay 'none'; camera 'none'; display-capture 'none'; document-domain 'none'; encrypted-media 'none'; fullscreen 'none'; geolocation 'none'; gyroscope 'none'; magnetometer 'none'; microphone 'none'; midi 'none'; payment 'none'; picture-in-picture 'none'; speaker 'none'; sync-xhr 'none'; usb 'none'; vibrate 'none'; vr 'none'; wake-lock 'none'; webauthn 'none'; xr-spatial-tracking 'none'
   Referrer-Policy: no-referrer
-  Strict-Transport-Security: max-age=31536000
+  Strict-Transport-Security: max-age=31536000; includeSubDomains; preload
   X-Content-Type-Options: nosniff
   X-Frame-Options: DENY
   X-XSS-Protection: 1; mode=block