diff --git a/zfs.nix b/zfs.nix
index 8dd552d..8e5dbe9 100644
--- a/zfs.nix
+++ b/zfs.nix
@@ -25,10 +25,13 @@ in
 
   boot.kernelParams =
     let
-      mb = 20000;
+      gb = 20;
+      mb = gb * 1000;
+      kb = mb * 1000;
+      b = kb * 1000;
     in
     [
-      "zfs.zfs_arc_max=${builtins.toString (mb * 1000000)}"
+      "zfs.zfs_arc_max=${builtins.toString b}"
     ];
 
   boot.supportedFilesystems = [ "zfs" ];