diff --git a/nixos/modules/system/boot/networkd.nix b/nixos/modules/system/boot/networkd.nix
index 44210c8a82c6..43fa93aadf1c 100644
--- a/nixos/modules/system/boot/networkd.nix
+++ b/nixos/modules/system/boot/networkd.nix
@@ -1017,6 +1017,7 @@ let
           "BootServerAddress"
           "BootServerName"
           "BootFilename"
+          "IPv6OnlyPreferredSec"
         ])
         (assertInt "PoolOffset")
         (assertMinimum "PoolOffset" 0)