diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 26ff4026cd..20e0ebfa30 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -725,8 +725,7 @@ cross-version-config-tests:
     # Run the setup phase of all system tests in the most recently tagged BIND 9
     # release using the binaries built for the current BIND 9 version.  This
     # intends to detect obvious backward compatibility issues with the latter.
-    - >
-      echo "${CI_PROJECT_DIR}" > isctest/vars/.ac_vars/TOP_BUILDDIR
+    - sed -i "s|f\"{AC_VARS\['TOP_BUILDDIR'\]}|\"$CI_PROJECT_DIR|g" isctest/vars/basic.py
     - >
       "$PYTEST" --setup-only --junit-xml="$CI_PROJECT_DIR"/junit.xml -n "${TEST_PARALLEL_JOBS:-1}"
   needs: