diff --git a/modules/base/nix.nix b/modules/base/nix.nix
index 86743a5..fde4a69 100644
--- a/modules/base/nix.nix
+++ b/modules/base/nix.nix
@@ -5,7 +5,7 @@
     gc = {
       automatic = true;
       dates = "weekly";
-      options = "--delete-older-than 15";
+      options = "--delete-older-than 15d";
     };
   };
 }