diff --git a/lib/Command/TransferLegacyRows.php b/lib/Command/TransferLegacyRows.php
index 49b255e4c..cd42cec1d 100644
--- a/lib/Command/TransferLegacyRows.php
+++ b/lib/Command/TransferLegacyRows.php
@@ -162,7 +162,7 @@ private function transferTable(Table $table, OutputInterface $output): void {
 	 * @param OutputInterface $output
 	 * @return void
 	 */
-	private function deleteDataForTables(array $tables, OutputInterface $output) {
+	private function deleteDataForTables(array $tables, OutputInterface $output): void {
 		$output->writeln("Start deleting data for tables that should be transferred.");
 		foreach ($tables as $table) {
 			try {