diff --git a/nixos/modules/services/games/minetest-server.nix b/nixos/modules/services/games/minetest-server.nix
index f52079fc1ef..2111c970d4f 100644
--- a/nixos/modules/services/games/minetest-server.nix
+++ b/nixos/modules/services/games/minetest-server.nix
@@ -4,7 +4,7 @@ with lib;
 
 let
   cfg   = config.services.minetest-server;
-  flag  = val: name: if val != null then "--${name} ${val} " else "";
+  flag  = val: name: if val != null then "--${name} ${toString val} " else "";
   flags = [
     (flag cfg.gameId "gameid")
     (flag cfg.world "world")