diff --git a/lib/fudo/initrd-network.nix b/lib/fudo/initrd-network.nix
index 8b00a5c..af58c85 100644
--- a/lib/fudo/initrd-network.nix
+++ b/lib/fudo/initrd-network.nix
@@ -10,7 +10,7 @@ let
   concatLists = lsts: concatMap (i: i) lsts;
 
   gen-sshfp-records-pkg = hostname: pubkey: let
-    pubkey-file = writeTextFile {
+    pubkey-file = builtins.writeTextFile {
       name = "${hostname}-initrd-ssh-pubkey";
       text = pubkey;
     };