diff --git a/module/configuration.nix b/module/configuration.nix
index a466f68..3728cae 100644
--- a/module/configuration.nix
+++ b/module/configuration.nix
@@ -1,6 +1,10 @@
 { hostname, username }:
 {
   nix = {
+    gc = {
+      automatic = true;
+      options = "--delete-older-than 30d";
+    };
     optimise.automatic = true;
     settings = {
       builders-use-substitutes = true;