diff --git a/build/rector-downgrade.php b/build/rector-downgrade.php
index db813797be..e3e5e5627d 100644
--- a/build/rector-downgrade.php
+++ b/build/rector-downgrade.php
@@ -28,6 +28,7 @@
 	$config->paths($cache->restore());
 	$config->phpVersion($targetPhpVersionId);
 	$config->skip(RectorCache::SKIP_PATHS);
+	$config->disableParallel();
 
 	if ($targetPhpVersionId < 80100) {
 		$config->rule(DowngradeReadonlyPropertyRector::class);