diff --git a/nixos/modules/services/cluster/kubernetes.nix b/nixos/modules/services/cluster/kubernetes.nix
index 9ccc7295019..25eaf70850c 100644
--- a/nixos/modules/services/cluster/kubernetes.nix
+++ b/nixos/modules/services/cluster/kubernetes.nix
@@ -45,7 +45,7 @@ let
   cniConfig = pkgs.buildEnv {
     name = "kubernetes-cni-config";
     paths = imap (i: entry:
-      pkgs.writeTextDir "${10+i}-${entry.type}.conf" (builtins.toJSON entry)
+      pkgs.writeTextDir "${toString (10+i)}-${entry.type}.conf" (builtins.toJSON entry)
     ) cfg.kubelet.cni.config;
   };