diff --git a/nixos/modules/services/backup/tsm.nix b/nixos/modules/services/backup/tsm.nix
index d138e163e34f..0017a6f69c16 100644
--- a/nixos/modules/services/backup/tsm.nix
+++ b/nixos/modules/services/backup/tsm.nix
@@ -87,16 +87,35 @@ in
       environment.DSM_LOG = "/var/log/tsm-backup/";
       # TSM needs a HOME dir to store certificates.
       environment.HOME = "/var/lib/tsm-backup";
-      # for exit status description see
-      # https://www.ibm.com/docs/en/spectrum-protect/8.1.13?topic=clients-client-return-codes
-      serviceConfig.SuccessExitStatus = "4 8";
-      # The `-se` option must come after the command.
-      # The `-optfile` option suppresses a `dsm.opt`-not-found warning.
-      serviceConfig.ExecStart =
-        "${cfgPrg.wrappedPackage}/bin/dsmc ${cfg.command} -se='${cfg.servername}' -optfile=/dev/null";
-      serviceConfig.LogsDirectory = "tsm-backup";
-      serviceConfig.StateDirectory = "tsm-backup";
-      serviceConfig.StateDirectoryMode = "0750";
+      serviceConfig = {
+        # for exit status description see
+        # https://www.ibm.com/docs/en/spectrum-protect/8.1.13?topic=clients-client-return-codes
+        SuccessExitStatus = "4 8";
+        # The `-se` option must come after the command.
+        # The `-optfile` option suppresses a `dsm.opt`-not-found warning.
+        ExecStart =
+          "${cfgPrg.wrappedPackage}/bin/dsmc ${cfg.command} -se='${cfg.servername}' -optfile=/dev/null";
+        LogsDirectory = "tsm-backup";
+        StateDirectory = "tsm-backup";
+        StateDirectoryMode = "0750";
+        # systemd sandboxing
+        LockPersonality = true;
+        NoNewPrivileges = true;
+        PrivateDevices = true;
+        #PrivateTmp = true;  # would break backup of {/var,}/tmp
+        #PrivateUsers = true;  # would block backup of /home/*
+        ProtectClock = true;
+        ProtectControlGroups = true;
+        ProtectHome = "read-only";
+        ProtectHostname = true;
+        ProtectKernelLogs = true;
+        ProtectKernelModules = true;
+        ProtectKernelTunables = true;
+        ProtectProc = "noaccess";
+        ProtectSystem = "strict";
+        RestrictNamespaces = true;
+        RestrictSUIDSGID = true;
+      };
       startAt = mkIf (cfg.autoTime!=null) cfg.autoTime;
     };
   };