diff --git a/nixos/modules/services/mail/rmilter.nix b/nixos/modules/services/mail/rmilter.nix
index e27b38bc0e2e..8f18b929c114 100644
--- a/nixos/modules/services/mail/rmilter.nix
+++ b/nixos/modules/services/mail/rmilter.nix
@@ -203,7 +203,7 @@ milter_default_action = accept
         PermissionsStartOnly = true;
         Restart = "always";
         RuntimeDirectory = "rmilter";
-        RuntimeDirectoryPermissions="0755";
+        RuntimeDirectoryMode = "0755";
       };
 
     };