diff --git a/lib/Command/CollectionDelete.php b/lib/Command/CollectionDelete.php
index 8975ec16..98107a3e 100644
--- a/lib/Command/CollectionDelete.php
+++ b/lib/Command/CollectionDelete.php
@@ -50,7 +50,7 @@ protected function configure() {
 	 *
 	 * @return int
 	 */
-	protected function execute(InputInterface $input, OutputInterface $output) {
+	protected function execute(InputInterface $input, OutputInterface $output): int {
 		$collection = $input->getArgument('name');
 		if (!$this->collectionService->hasCollection($collection)) {
 			throw new CollectionArgumentException('unknown collection');
diff --git a/lib/Command/CollectionList.php b/lib/Command/CollectionList.php
index f65fa575..d6908517 100644
--- a/lib/Command/CollectionList.php
+++ b/lib/Command/CollectionList.php
@@ -40,7 +40,7 @@ protected function configure() {
 	 *
 	 * @return int
 	 */
-	protected function execute(InputInterface $input, OutputInterface $output) {
+	protected function execute(InputInterface $input, OutputInterface $output): int {
 		$collections = $this->collectionService->getCollections();
 		$output->writeln('found ' . sizeof($collections) . ' collection(s)');
 
diff --git a/lib/Command/DocumentPlatform.php b/lib/Command/DocumentPlatform.php
index 32cfc29b..6d89c780 100644
--- a/lib/Command/DocumentPlatform.php
+++ b/lib/Command/DocumentPlatform.php
@@ -44,7 +44,7 @@ protected function configure() {
 	 *
 	 * @throws Exception
 	 */
-	protected function execute(InputInterface $input, OutputInterface $output) {
+	protected function execute(InputInterface $input, OutputInterface $output): int {
 		$providerId = $input->getArgument('providerId');
 		$documentId = $input->getArgument('documentId');
 
diff --git a/lib/Command/DocumentProvider.php b/lib/Command/DocumentProvider.php
index a7e73877..5f2f631e 100644
--- a/lib/Command/DocumentProvider.php
+++ b/lib/Command/DocumentProvider.php
@@ -47,7 +47,7 @@ protected function configure() {
 	 *
 	 * @throws Exception
 	 */
-	protected function execute(InputInterface $input, OutputInterface $output) {
+	protected function execute(InputInterface $input, OutputInterface $output): int {
 		$providerId = $input->getArgument('providerId');
 		$documentId = $input->getArgument('documentId');
 		$userId = $input->getArgument('userId');
diff --git a/lib/Command/DocumentStatus.php b/lib/Command/DocumentStatus.php
index af0905b7..10b2bba5 100644
--- a/lib/Command/DocumentStatus.php
+++ b/lib/Command/DocumentStatus.php
@@ -56,7 +56,7 @@ protected function configure() {
 	 *
 	 * @throws Exception
 	 */
-	protected function execute(InputInterface $input, OutputInterface $output) {
+	protected function execute(InputInterface $input, OutputInterface $output): int {
 		$providerId = $input->getArgument('provider');
 		$documentId = $input->getArgument('document');
 		$value = $input->getOption('value');
diff --git a/lib/Command/Live.php b/lib/Command/Live.php
index 6381df26..2049629e 100644
--- a/lib/Command/Live.php
+++ b/lib/Command/Live.php
@@ -129,10 +129,9 @@ protected function configure(): void {
 	 * @param InputInterface $input
 	 * @param OutputInterface $output
 	 *
-	 * @return int|null|void
 	 * @throws Exception
 	 */
-	protected function execute(InputInterface $input, OutputInterface $output) {
+	protected function execute(InputInterface $input, OutputInterface $output): int {
 		if (!$input->getOption('service') && !$input->getOption('no-readline')) {
 			try {
 				/** do not get stuck while waiting interactive input */
diff --git a/lib/Command/Search.php b/lib/Command/Search.php
index 0aebf1c6..0f522b5a 100644
--- a/lib/Command/Search.php
+++ b/lib/Command/Search.php
@@ -46,7 +46,7 @@ protected function configure() {
 	 * @return int
 	 * @throws Exception
 	 */
-	protected function execute(InputInterface $input, OutputInterface $output) {
+	protected function execute(InputInterface $input, OutputInterface $output): int {
 		$searchRequest = new SearchRequest();
 		$searchRequest->importFromArray(
 			[
diff --git a/lib/Command/Stop.php b/lib/Command/Stop.php
index 9d26b96e..5899d42d 100644
--- a/lib/Command/Stop.php
+++ b/lib/Command/Stop.php
@@ -38,7 +38,7 @@ protected function configure() {
 	 *
 	 * @return int
 	 */
-	protected function execute(InputInterface $input, OutputInterface $output) {
+	protected function execute(InputInterface $input, OutputInterface $output): int {
 		$output->writeln('stopping all running indexes');
 
 		$this->runningService->forceStop();