diff --git a/defaults/nix.nix b/defaults/nix.nix
index 2f1364a..6825299 100644
--- a/defaults/nix.nix
+++ b/defaults/nix.nix
@@ -25,6 +25,13 @@ in
     # source: https://nix.dev/manual/nix/2.26/command-ref/new-cli/nix3-store-optimise
     nix.settings.auto-optimise-store = true;
 
+    # trigger the garbage collector automatically
+    # when free space in /nix/store goes below this
+    nix.settings.min-free = 1000000000; # 1GB
+    # free up to this many bytes in an automatic invocation
+    # to avoid it taking too long
+    nix.settings.max-free = 5000000000; # 5GB
+
     environment.systemPackages =
       with pkgs;
       lib.mkIf config.nixowos.allowAddingPackages [