diff --git a/nix/module.nix b/nix/module.nix
index 494335b..1bb8cdc 100644
--- a/nix/module.nix
+++ b/nix/module.nix
@@ -113,6 +113,7 @@ in {
 
     systemd.services."pi-air-quality-monitor" = let
       globalEnv = pkgs.writeText "global.env" ''
+        PORT=${toString cfg.settings.port}
         SERIAL_DEVICE=${cfg.settings.serialPort}
       '';