diff --git a/nixos/modules/services/monitoring/mackerel-agent.nix b/nixos/modules/services/monitoring/mackerel-agent.nix
index d218c18c4354..0908ea9ca68e 100644
--- a/nixos/modules/services/monitoring/mackerel-agent.nix
+++ b/nixos/modules/services/monitoring/mackerel-agent.nix
@@ -98,7 +98,7 @@ in {
         RuntimeDirectory = "mackerel-agent";
         StateDirectory = "mackerel-agent";
         ExecStart = "${pkgs.mackerel-agent}/bin/mackerel-agent supervise";
-        ExecStopPost = mkIf cfg.autoRetirement "${pkg.mackerel-agent}/bin/mackerel-agent retire -force";
+        ExecStopPost = mkIf cfg.autoRetirement "${pkgs.mackerel-agent}/bin/mackerel-agent retire -force";
         ExecReload = "${pkgs.coreutils}/bin/kill -HUP $MAINPID";
         LimitNOFILE = mkDefault 65536;
         LimitNPROC = mkDefault 65536;