diff --git a/core/Command/App/Disable.php b/core/Command/App/Disable.php
index c5abc6c95cf01..53a1376534249 100644
--- a/core/Command/App/Disable.php
+++ b/core/Command/App/Disable.php
@@ -83,7 +83,7 @@ private function disableApp(string $appId, OutputInterface $output): void {
 	 * @param CompletionContext $context
 	 * @return string[]
 	 */
-	public function completeOptionValues($optionName, CompletionContext $context) {
+	public function completeOptionValues($optionName, CompletionContext $context): array {
 		return [];
 	}
 
@@ -92,7 +92,7 @@ public function completeOptionValues($optionName, CompletionContext $context) {
 	 * @param CompletionContext $context
 	 * @return string[]
 	 */
-	public function completeArgumentValues($argumentName, CompletionContext $context) {
+	public function completeArgumentValues($argumentName, CompletionContext $context): array {
 		if ($argumentName === 'app-id') {
 			return array_diff(\OC_App::getEnabledApps(true, true), $this->appManager->getAlwaysEnabledApps());
 		}
diff --git a/core/Command/App/Enable.php b/core/Command/App/Enable.php
index c3ab8be38cea4..624b31521ad74 100644
--- a/core/Command/App/Enable.php
+++ b/core/Command/App/Enable.php
@@ -146,7 +146,7 @@ private function resolveGroupIds(array $groupIds): array {
 	 * @param CompletionContext $context
 	 * @return string[]
 	 */
-	public function completeOptionValues($optionName, CompletionContext $context) {
+	public function completeOptionValues($optionName, CompletionContext $context): array {
 		if ($optionName === 'groups') {
 			return array_map(function (IGroup $group) {
 				return $group->getGID();
@@ -160,7 +160,7 @@ public function completeOptionValues($optionName, CompletionContext $context) {
 	 * @param CompletionContext $context
 	 * @return string[]
 	 */
-	public function completeArgumentValues($argumentName, CompletionContext $context) {
+	public function completeArgumentValues($argumentName, CompletionContext $context): array {
 		if ($argumentName === 'app-id') {
 			$allApps = \OC_App::getAllApps();
 			return array_diff($allApps, \OC_App::getEnabledApps(true, true));
diff --git a/core/Command/App/GetPath.php b/core/Command/App/GetPath.php
index 2ec723851912a..ea614070e7d0d 100644
--- a/core/Command/App/GetPath.php
+++ b/core/Command/App/GetPath.php
@@ -29,7 +29,7 @@
 use Symfony\Component\Console\Output\OutputInterface;
 
 class GetPath extends Base {
-	protected function configure() {
+	protected function configure(): void {
 		parent::configure();
 
 		$this
@@ -67,7 +67,7 @@ protected function execute(InputInterface $input, OutputInterface $output): int
 	 * @param CompletionContext $context
 	 * @return string[]
 	 */
-	public function completeArgumentValues($argumentName, CompletionContext $context) {
+	public function completeArgumentValues($argumentName, CompletionContext $context): array {
 		if ($argumentName === 'app') {
 			return \OC_App::getAllApps();
 		}
diff --git a/core/Command/App/Install.php b/core/Command/App/Install.php
index d87439b366480..2d02fff4dbfd8 100644
--- a/core/Command/App/Install.php
+++ b/core/Command/App/Install.php
@@ -36,7 +36,7 @@
 use Symfony\Component\Console\Output\OutputInterface;
 
 class Install extends Command {
-	protected function configure() {
+	protected function configure(): void {
 		$this
 			->setName('app:install')
 			->setDescription('install an app')
diff --git a/core/Command/App/ListApps.php b/core/Command/App/ListApps.php
index 24856304afc39..2db781418e591 100644
--- a/core/Command/App/ListApps.php
+++ b/core/Command/App/ListApps.php
@@ -39,7 +39,7 @@ public function __construct(
 		parent::__construct();
 	}
 
-	protected function configure() {
+	protected function configure(): void {
 		parent::configure();
 
 		$this
@@ -98,7 +98,7 @@ protected function execute(InputInterface $input, OutputInterface $output): int
 	 * @param OutputInterface $output
 	 * @param array $items
 	 */
-	protected function writeAppList(InputInterface $input, OutputInterface $output, $items) {
+	protected function writeAppList(InputInterface $input, OutputInterface $output, $items): void {
 		switch ($input->getOption('output')) {
 			case self::OUTPUT_FORMAT_PLAIN:
 				$output->writeln('Enabled:');
@@ -119,7 +119,7 @@ protected function writeAppList(InputInterface $input, OutputInterface $output,
 	 * @param CompletionContext $context
 	 * @return array
 	 */
-	public function completeOptionValues($optionName, CompletionContext $context) {
+	public function completeOptionValues($optionName, CompletionContext $context): array {
 		if ($optionName === 'shipped') {
 			return ['true', 'false'];
 		}
@@ -131,7 +131,7 @@ public function completeOptionValues($optionName, CompletionContext $context) {
 	 * @param CompletionContext $context
 	 * @return string[]
 	 */
-	public function completeArgumentValues($argumentName, CompletionContext $context) {
+	public function completeArgumentValues($argumentName, CompletionContext $context): array {
 		return [];
 	}
 }
diff --git a/core/Command/App/Remove.php b/core/Command/App/Remove.php
index 522ddc20e07c0..5fa05079bd824 100644
--- a/core/Command/App/Remove.php
+++ b/core/Command/App/Remove.php
@@ -47,7 +47,7 @@ public function __construct(
 		parent::__construct();
 	}
 
-	protected function configure() {
+	protected function configure(): void {
 		$this
 			->setName('app:remove')
 			->setDescription('remove an app')
@@ -124,7 +124,7 @@ protected function execute(InputInterface $input, OutputInterface $output): int
 	 * @param CompletionContext $context
 	 * @return string[]
 	 */
-	public function completeOptionValues($optionName, CompletionContext $context) {
+	public function completeOptionValues($optionName, CompletionContext $context): array {
 		return [];
 	}
 
@@ -133,7 +133,7 @@ public function completeOptionValues($optionName, CompletionContext $context) {
 	 * @param CompletionContext $context
 	 * @return string[]
 	 */
-	public function completeArgumentValues($argumentName, CompletionContext $context) {
+	public function completeArgumentValues($argumentName, CompletionContext $context): array {
 		if ($argumentName === 'app-id') {
 			return \OC_App::getAllApps();
 		}
diff --git a/core/Command/App/Update.php b/core/Command/App/Update.php
index 7d47034398fdb..c089416744f49 100644
--- a/core/Command/App/Update.php
+++ b/core/Command/App/Update.php
@@ -45,7 +45,7 @@ public function __construct(
 		parent::__construct();
 	}
 
-	protected function configure() {
+	protected function configure(): void {
 		$this
 			->setName('app:update')
 			->setDescription('update an app or all apps')