diff --git a/nixos/modules/services/continuous-integration/hydra/default.nix b/nixos/modules/services/continuous-integration/hydra/default.nix
index 2206ac522e4a..0103cd723d2f 100644
--- a/nixos/modules/services/continuous-integration/hydra/default.nix
+++ b/nixos/modules/services/continuous-integration/hydra/default.nix
@@ -280,6 +280,8 @@ in
       keep-outputs = true
       keep-derivations = true
 
+
+    '' + optionalString (versionOlder (getVersion config.nix.package.out) "2.4pre") ''
       # The default (`true') slows Nix down a lot since the build farm
       # has so many GC roots.
       gc-check-reachability = false