diff --git a/nixos/lib/testing.nix b/nixos/lib/testing.nix
index 9339ba78ff0c..532fff681d37 100644
--- a/nixos/lib/testing.nix
+++ b/nixos/lib/testing.nix
@@ -113,8 +113,7 @@ rec {
             --add-flags "''${vms[*]}" \
             ${lib.optionalString enableOCR
               "--prefix PATH : '${ocrProg}/bin:${imagemagick}/bin'"} \
-            --run "testScript=\"\$(cat $out/test-script)\"" \
-            --set testScript '$testScript' \
+            --run "export testScript=\"\$(cat $out/test-script)\"" \
             --set VLANS '${toString vlans}'
           ln -s ${testDriver}/bin/nixos-test-driver $out/bin/nixos-run-vms
           wrapProgram $out/bin/nixos-run-vms \