diff --git a/nixbld-etc-nixos/configuration.nix b/nixbld-etc-nixos/configuration.nix
index 4dbf734..30df87f 100644
--- a/nixbld-etc-nixos/configuration.nix
+++ b/nixbld-etc-nixos/configuration.nix
@@ -759,6 +759,9 @@ in
 
   services.rt = {
     enable = true;
+    package = pkgs.rt.overrideAttrs(oa: {
+      patches = oa.patches or [] ++ [ ./rt-session.patch ];
+    });
     organization = "M-Labs";
     domain = "rt.m-labs.hk";
     rtName = "Helpdesk";
diff --git a/nixbld-etc-nixos/rt-session.patch b/nixbld-etc-nixos/rt-session.patch
new file mode 100644
index 0000000..9e7bb22
--- /dev/null
+++ b/nixbld-etc-nixos/rt-session.patch
@@ -0,0 +1,11 @@
+diff '--color=auto' -Naur rt-5.0.1/lib/RT/Interface/Web.pm rtpatched/lib/RT/Interface/Web.pm
+--- rt-5.0.1/lib/RT/Interface/Web.pm	1970-01-01 08:00:01.000000000 +0800
++++ rtpatched/lib/RT/Interface/Web.pm	2021-08-12 13:34:08.870669968 +0800
+@@ -948,6 +948,7 @@
+         -path     => RT->Config->Get('WebPath'),
+         -secure   => ( RT->Config->Get('WebSecureCookies') ? 1 : 0 ),
+         -httponly => ( RT->Config->Get('WebHttpOnlyCookies') ? 1 : 0 ),
++        -expires => '+6M',
+     );
+ 
+     $HTML::Mason::Commands::r->err_headers_out->{'Set-Cookie'} = $cookie->as_string;