diff --git a/default.nix b/default.nix
index 70098fb..bfcd93b 100644
--- a/default.nix
+++ b/default.nix
@@ -5,7 +5,7 @@
 # containing 'defaultNix' (to be used in 'default.nix'), 'shellNix'
 # (to be used in 'shell.nix').
 
-{ src }:
+{ src, system ? builtins.currentSystem or "unknown-system" }:
 
 let
 
@@ -69,8 +69,6 @@ let
 
   result = callFlake src' (lockFile.inputs);
 
-  system = builtins.currentSystem or "unknown-system";
-
 in
   assert lockFile.version == 4;