diff --git a/nixos/modules/tasks/filesystems/nfs.nix b/nixos/modules/tasks/filesystems/nfs.nix
index f7f2d9658069..45c1119215e5 100644
--- a/nixos/modules/tasks/filesystems/nfs.nix
+++ b/nixos/modules/tasks/filesystems/nfs.nix
@@ -13,7 +13,7 @@ let
   idmapdConfFile = pkgs.writeText "idmapd.conf" ''
     [General]
     Pipefs-Directory = ${rpcMountpoint}
-    ${optionalString (config.networking.domain != "")
+    ${optionalString (config.networking.domain != null)
       "Domain = ${config.networking.domain}"}
 
     [Mapping]