diff --git a/nixos/modules/services/monitoring/prometheus/alertmanager.nix b/nixos/modules/services/monitoring/prometheus/alertmanager.nix
index 187b78de899f..2f3245e3286b 100644
--- a/nixos/modules/services/monitoring/prometheus/alertmanager.nix
+++ b/nixos/modules/services/monitoring/prometheus/alertmanager.nix
@@ -153,7 +153,7 @@ let
           after    = [ "network.target" ];
           script = ''
             ${amCfg.package}/bin/alertmanager \
-              ${concatStringsSep " \\\n  " cmdlineArgs}
+              ${concatStringsSep " \\\n  " (mkCmdlineArgs amCfg)}
           '';
           serviceConfig = {
             User = amCfg.user;