diff --git a/nixos/lib/make-system-tarball.nix b/nixos/lib/make-system-tarball.nix
index 3bd891fdbc2..a2a0340a6bd 100644
--- a/nixos/lib/make-system-tarball.nix
+++ b/nixos/lib/make-system-tarball.nix
@@ -16,6 +16,9 @@
   # symlink to `object' that will be added to the tarball.
   storeContents ? []
 
+  # Extra commands to be executed before archiving files
+, extraCommands ? ""
+
   # Extra tar arguments
 , extraArgs ? ""
 }:
@@ -25,7 +28,7 @@ stdenv.mkDerivation {
   builder = ./make-system-tarball.sh;
   buildInputs = [perl xz];
 
-  inherit fileName pathsFromGraph extraArgs;
+  inherit fileName pathsFromGraph extraArgs extraCommands;
 
   # !!! should use XML.
   sources = map (x: x.source) contents;
diff --git a/nixos/lib/make-system-tarball.sh b/nixos/lib/make-system-tarball.sh
index 2eb668115a6..e04455e889b 100644
--- a/nixos/lib/make-system-tarball.sh
+++ b/nixos/lib/make-system-tarball.sh
@@ -33,7 +33,7 @@ for i in $storePaths; do
 done
 
 
-# TODO tar ruxo 
+# TODO tar ruxo
 # Also include a manifest of the closures in a format suitable for
 # nix-store --load-db.
 printRegistration=1 perl $pathsFromGraph closure-* > nix-path-registration
@@ -48,6 +48,8 @@ for ((n = 0; n < ${#objects[*]}; n++)); do
     fi
 done
 
+$extraCommands
+
 mkdir -p $out/tarball
 
 tar cvJf $out/tarball/$fileName.tar.xz * $extraArgs