diff --git a/hydra-module.nix b/hydra-module.nix
index 276cb2ae..1bfb9a42 100644
--- a/hydra-module.nix
+++ b/hydra-module.nix
@@ -165,7 +165,7 @@ in
 
       buildMachinesFiles = mkOption {
         type = types.listOf types.path;
-        default = [ "/etc/nix/machines" ];
+        default = optional (config.nix.buildMachines != []) "/etc/nix/machines";
         example = [ "/etc/nix/machines" "/var/lib/hydra/provisioner/machines" ];
         description = "List of files containing build machines.";
       };