diff --git a/config/services/hydra/nix-config.nix b/config/services/hydra/nix-config.nix
index 6359fc5..b4a2faa 100644
--- a/config/services/hydra/nix-config.nix
+++ b/config/services/hydra/nix-config.nix
@@ -39,7 +39,10 @@
   });
   nix.distributedBuilds = true;
   nixpkgs.config.allowUnsupportedSystem = true;
-  nix.gc.options = lib.mkForce "--delete-older-than 90d";
+  nix.gc = {
+    dates = "monthly";
+    options = lib.mkForce "--delete-older-than 90d";
+  };
   nix.settings = {
     allowed-uris = [
       "github:"