diff --git a/nixos/lib/make-system-tarball.nix b/nixos/lib/make-system-tarball.nix
index 9fb77230cf63..f84fe8f5cbac 100644
--- a/nixos/lib/make-system-tarball.nix
+++ b/nixos/lib/make-system-tarball.nix
@@ -39,7 +39,9 @@ in
 
 stdenv.mkDerivation {
   name = "tarball";
-  builder = ./make-system-tarball.sh;
+  __structuredAttrs = true;
+
+  buildCommandPath = ./make-system-tarball.sh;
   nativeBuildInputs = extraInputs;
 
   inherit
@@ -49,11 +51,9 @@ stdenv.mkDerivation {
     compressCommand
     ;
 
-  # !!! should use XML.
   sources = map (x: x.source) contents;
   targets = map (x: x.target) contents;
 
-  # !!! should use XML.
   inherit symlinks objects;
 
   closureInfo = closureInfo {
diff --git a/nixos/lib/make-system-tarball.sh b/nixos/lib/make-system-tarball.sh
index 8fadc79a13dc..ea24dcf9842d 100644
--- a/nixos/lib/make-system-tarball.sh
+++ b/nixos/lib/make-system-tarball.sh
@@ -1,10 +1,3 @@
-sources_=($sources)
-targets_=($targets)
-
-objects=($objects)
-symlinks=($symlinks)
-
-
 # Remove the initial slash from a path, since genisofs likes it that way.
 stripSlash() {
     res="$1"
@@ -12,10 +5,10 @@ stripSlash() {
 }
 
 # Add the individual files.
-for ((i = 0; i < ${#targets_[@]}; i++)); do
-    stripSlash "${targets_[$i]}"
+for ((i = 0; i < ${#targets[@]}; i++)); do
+    stripSlash "${targets[$i]}"
     mkdir -p "$(dirname "$res")"
-    cp -a "${sources_[$i]}" "$res"
+    cp -a "${sources[$i]}" "$res"
 done