diff --git a/pkgs/kubenix.nix b/pkgs/kubenix.nix
index 88555ca..dfb7215 100644
--- a/pkgs/kubenix.nix
+++ b/pkgs/kubenix.nix
@@ -36,11 +36,10 @@ symlinkJoin {
   passthru.manifest = result;
 
   postBuild = ''
-    export DIFF="${diff}"
     wrapProgram $out/bin/kubenix \
       --set PATH "$out/bin" \
-      --set KUBECONFIG "${kubeconfig}" \
-      --set KUBECTL_EXTERNAL_DIFF "''${DIFF}" \
-      --set MANIFEST "${result}"
+      --run 'export KUBECONFIG=''${KUBECONFIG:-${kubeconfig}}' \
+      --set KUBECTL_EXTERNAL_DIFF '${diff}' \
+      --set MANIFEST '${result}'
   '';
 }