diff --git a/nix/nixos/cardano-node-service.nix b/nix/nixos/cardano-node-service.nix
index fbc55f42aa5..25402447ba2 100644
--- a/nix/nixos/cardano-node-service.nix
+++ b/nix/nixos/cardano-node-service.nix
@@ -56,7 +56,7 @@ let
   selectTopology = i:
     if cfg.topology != null
     then cfg.topology
-    else toFile "topology.yaml" (toJSON (if (cfg.useNewTopology) then assertNewTopology i else oldTopology i));
+    else toFile "topology.json" (toJSON (if (cfg.useNewTopology) then assertNewTopology i else oldTopology i));
 
   topology = i:
     if cfg.useSystemdReload