diff --git a/apps/admin_audit/lib/Actions/Action.php b/apps/admin_audit/lib/Actions/Action.php
index 28e3281988..42540c3047 100644
--- a/apps/admin_audit/lib/Actions/Action.php
+++ b/apps/admin_audit/lib/Actions/Action.php
@@ -50,7 +50,7 @@ class Action {
 	public function log(string $text,
 						array $params,
 						array $elements,
-						bool $obfuscateParameters = false) {
+						bool $obfuscateParameters = false): void {
 		foreach ($elements as $element) {
 			if (!isset($params[$element])) {
 				if ($obfuscateParameters) {
diff --git a/apps/admin_audit/lib/Actions/AppManagement.php b/apps/admin_audit/lib/Actions/AppManagement.php
index e0d447b1d6..d4340a1c7b 100644
--- a/apps/admin_audit/lib/Actions/AppManagement.php
+++ b/apps/admin_audit/lib/Actions/AppManagement.php
@@ -32,7 +32,7 @@ class AppManagement extends Action {
 	/**
 	 * @param string $appName
 	 */
-	public function enableApp(string $appName) {
+	public function enableApp(string $appName): void {
 		$this->log('App "%s" enabled',
 			['app' => $appName],
 			['app']
@@ -43,7 +43,7 @@ class AppManagement extends Action {
 	 * @param string $appName
 	 * @param string[] $groups
 	 */
-	public function enableAppForGroups(string $appName, array $groups) {
+	public function enableAppForGroups(string $appName, array $groups): void {
 		$this->log('App "%1$s" enabled for groups: %2$s',
 			['app' => $appName, 'groups' => implode(', ', $groups)],
 			['app', 'groups']
@@ -53,7 +53,7 @@ class AppManagement extends Action {
 	/**
 	 * @param string $appName
 	 */
-	public function disableApp(string $appName) {
+	public function disableApp(string $appName): void {
 		$this->log('App "%s" disabled',
 			['app' => $appName],
 			['app']
diff --git a/apps/admin_audit/lib/Actions/Auth.php b/apps/admin_audit/lib/Actions/Auth.php
index f4350dbe86..9e0ed67474 100644
--- a/apps/admin_audit/lib/Actions/Auth.php
+++ b/apps/admin_audit/lib/Actions/Auth.php
@@ -33,7 +33,7 @@ namespace OCA\AdminAudit\Actions;
  * @package OCA\AdminAudit\Actions
  */
 class Auth extends Action {
-	public function loginAttempt(array $params) {
+	public function loginAttempt(array $params): void {
 		$this->log(
 			'Login attempt: "%s"',
 			$params,
@@ -44,7 +44,7 @@ class Auth extends Action {
 		);
 	}
 
-	public function loginSuccessful(array $params) {
+	public function loginSuccessful(array $params): void {
 		$this->log(
 			'Login successful: "%s"',
 			$params,
@@ -55,7 +55,7 @@ class Auth extends Action {
 		);
 	}
 
-	public function logout(array $params) {
+	public function logout(array $params): void {
 		$this->log(
 			'Logout occurred',
 			[],
diff --git a/apps/admin_audit/lib/Actions/Console.php b/apps/admin_audit/lib/Actions/Console.php
index 5b2eb11da3..ad8b8e2d0b 100644
--- a/apps/admin_audit/lib/Actions/Console.php
+++ b/apps/admin_audit/lib/Actions/Console.php
@@ -32,7 +32,7 @@ class Console extends Action {
 	/**
 	 * @param $arguments
 	 */
-	public function runCommand(array $arguments) {
+	public function runCommand(array $arguments): void {
 		if (!isset($arguments[1]) || $arguments[1] === '_completion') {
 			// Don't log autocompletion
 			return;
diff --git a/apps/admin_audit/lib/Actions/Files.php b/apps/admin_audit/lib/Actions/Files.php
index 9b3f9fe755..79ac57927b 100644
--- a/apps/admin_audit/lib/Actions/Files.php
+++ b/apps/admin_audit/lib/Actions/Files.php
@@ -38,7 +38,7 @@ class Files extends Action {
 	 *
 	 * @param array $params
 	 */
-	public function read(array $params) {
+	public function read(array $params): void {
 		$this->log(
 			'File accessed: "%s"',
 			$params,
@@ -53,7 +53,7 @@ class Files extends Action {
 	 *
 	 * @param array $params
 	 */
-	public function rename(array $params) {
+	public function rename(array $params): void {
 		$this->log(
 			'File renamed: "%s" to "%s"',
 			$params,
@@ -69,7 +69,7 @@ class Files extends Action {
 	 *
 	 * @param array $params
 	 */
-	public function create(array $params) {
+	public function create(array $params): void {
 		if ($params['path'] === '/' || $params['path'] === '' || $params['path'] === null) {
 			return;
 		}
@@ -88,7 +88,7 @@ class Files extends Action {
 	 *
 	 * @param array $params
 	 */
-	public function copy(array $params) {
+	public function copy(array $params): void {
 		$this->log(
 			'File copied: "%s" to "%s"',
 			$params,
@@ -104,7 +104,7 @@ class Files extends Action {
 	 *
 	 * @param array $params
 	 */
-	public function write(array $params) {
+	public function write(array $params): void {
 		if ($params['path'] === '/' || $params['path'] === '' || $params['path'] === null) {
 			return;
 		}
@@ -123,7 +123,7 @@ class Files extends Action {
 	 *
 	 * @param array $params
 	 */
-	public function update(array $params) {
+	public function update(array $params): void {
 		$this->log(
 			'File updated: "%s"',
 			$params,
@@ -138,7 +138,7 @@ class Files extends Action {
 	 *
 	 * @param array $params
 	 */
-	public function delete(array $params) {
+	public function delete(array $params): void {
 		$this->log(
 			'File deleted: "%s"',
 			$params,
@@ -153,7 +153,7 @@ class Files extends Action {
 	 *
 	 * @param array $params
 	 */
-	public function preview(array $params) {
+	public function preview(array $params): void {
 		$this->log(
 			'Preview accessed: "%s" (width: "%s", height: "%s" crop: "%s", mode: "%s")',
 			$params,
diff --git a/apps/admin_audit/lib/Actions/GroupManagement.php b/apps/admin_audit/lib/Actions/GroupManagement.php
index daef3e5fbb..b73b8182f7 100644
--- a/apps/admin_audit/lib/Actions/GroupManagement.php
+++ b/apps/admin_audit/lib/Actions/GroupManagement.php
@@ -45,7 +45,7 @@ class GroupManagement extends Action {
 	 * @param IGroup $group
 	 * @param IUser $user
 	 */
-	public function addUser(IGroup $group, IUser $user) {
+	public function addUser(IGroup $group, IUser $user): void {
 		$this->log('User "%s" added to group "%s"',
 			[
 				'group' => $group->getGID(),
@@ -63,7 +63,7 @@ class GroupManagement extends Action {
 	 * @param IGroup $group
 	 * @param IUser $user
 	 */
-	public function removeUser(IGroup $group, IUser $user) {
+	public function removeUser(IGroup $group, IUser $user): void {
 		$this->log('User "%s" removed from group "%s"',
 			[
 				'group' => $group->getGID(),
@@ -74,13 +74,13 @@ class GroupManagement extends Action {
 			]
 		);
 	}
-	
+
 	/**
 	 * log create group to group event
 	 *
 	 * @param IGroup $group
 	 */
-	public function createGroup(IGroup $group) {
+	public function createGroup(IGroup $group): void {
 		$this->log('Group created: "%s"',
 			[
 				'group' => $group->getGID()
@@ -96,7 +96,7 @@ class GroupManagement extends Action {
 	 *
 	 * @param IGroup $group
 	 */
-	public function deleteGroup(IGroup $group) {
+	public function deleteGroup(IGroup $group): void {
 		$this->log('Group deleted: "%s"',
 			[
 				'group' => $group->getGID()
diff --git a/apps/admin_audit/lib/Actions/Security.php b/apps/admin_audit/lib/Actions/Security.php
index 9093e3a842..efb0819e7c 100644
--- a/apps/admin_audit/lib/Actions/Security.php
+++ b/apps/admin_audit/lib/Actions/Security.php
@@ -41,7 +41,7 @@ class Security extends Action {
 	 * @param IUser $user
 	 * @param array $params
 	 */
-	public function twofactorFailed(IUser $user, array $params) {
+	public function twofactorFailed(IUser $user, array $params): void {
 		$params['uid'] = $user->getUID();
 		$params['displayName'] = $user->getDisplayName();
 
@@ -62,7 +62,7 @@ class Security extends Action {
 	 * @param IUser $user
 	 * @param array $params
 	 */
-	public function twofactorSuccess(IUser $user, array $params) {
+	public function twofactorSuccess(IUser $user, array $params): void {
 		$params['uid'] = $user->getUID();
 		$params['displayName'] = $user->getDisplayName();
 
diff --git a/apps/admin_audit/lib/Actions/Sharing.php b/apps/admin_audit/lib/Actions/Sharing.php
index dc3ede0ae6..fb070c565a 100644
--- a/apps/admin_audit/lib/Actions/Sharing.php
+++ b/apps/admin_audit/lib/Actions/Sharing.php
@@ -43,7 +43,7 @@ class Sharing extends Action {
 	 *
 	 * @param array $params
 	 */
-	public function shared(array $params) {
+	public function shared(array $params): void {
 		if ($params['shareType'] === IShare::TYPE_LINK) {
 			$this->log(
 				'The %s "%s" with ID "%s" has been shared via link with permissions "%s" (Share ID: %s)',
@@ -168,7 +168,7 @@ class Sharing extends Action {
 	 *
 	 * @param array $params
 	 */
-	public function unshare(array $params) {
+	public function unshare(array $params): void {
 		if ($params['shareType'] === IShare::TYPE_LINK) {
 			$this->log(
 				'The %s "%s" with ID "%s" has been unshared (Share ID: %s)',
@@ -284,7 +284,7 @@ class Sharing extends Action {
 	 *
 	 * @param array $params
 	 */
-	public function updatePermissions(array $params) {
+	public function updatePermissions(array $params): void {
 		$this->log(
 			'The permissions of the shared %s "%s" with ID "%s" have been changed to "%s"',
 			$params,
@@ -302,7 +302,7 @@ class Sharing extends Action {
 	 *
 	 * @param array $params
 	 */
-	public function updatePassword(array $params) {
+	public function updatePassword(array $params): void {
 		$this->log(
 			'The password of the publicly shared %s "%s" with ID "%s" has been changed',
 			$params,
@@ -319,7 +319,7 @@ class Sharing extends Action {
 	 *
 	 * @param array $params
 	 */
-	public function updateExpirationDate(array $params) {
+	public function updateExpirationDate(array $params): void {
 		$this->log(
 			'The expiration date of the publicly shared %s with ID "%s" has been changed to "%s"',
 			$params,
@@ -336,7 +336,7 @@ class Sharing extends Action {
 	 *
 	 * @param array $params
 	 */
-	public function shareAccessed(array $params) {
+	public function shareAccessed(array $params): void {
 		$this->log(
 			'The shared %s with the token "%s" by "%s" has been accessed.',
 			$params,
diff --git a/apps/admin_audit/lib/Actions/Trashbin.php b/apps/admin_audit/lib/Actions/Trashbin.php
index a3e050a29f..d21eeb0ca3 100644
--- a/apps/admin_audit/lib/Actions/Trashbin.php
+++ b/apps/admin_audit/lib/Actions/Trashbin.php
@@ -29,13 +29,13 @@ declare(strict_types=1);
 namespace OCA\AdminAudit\Actions;
 
 class Trashbin extends Action {
-	public function delete(array $params) {
+	public function delete(array $params): void {
 		$this->log('File "%s" deleted from trash bin.',
 			['path' => $params['path']], ['path']
 		);
 	}
 
-	public function restore(array $params) {
+	public function restore(array $params): void {
 		$this->log('File "%s" restored from trash bin.',
 			['path' => $params['filePath']], ['path']
 		);
diff --git a/apps/admin_audit/lib/Actions/UserManagement.php b/apps/admin_audit/lib/Actions/UserManagement.php
index 33dd49f3b5..febadffef3 100644
--- a/apps/admin_audit/lib/Actions/UserManagement.php
+++ b/apps/admin_audit/lib/Actions/UserManagement.php
@@ -44,7 +44,7 @@ class UserManagement extends Action {
 	 *
 	 * @param array $params
 	 */
-	public function create(array $params) {
+	public function create(array $params): void {
 		$this->log(
 			'User created: "%s"',
 			$params,
@@ -59,7 +59,7 @@ class UserManagement extends Action {
 	 *
 	 * @param string $uid
 	 */
-	public function assign(string $uid) {
+	public function assign(string $uid): void {
 		$this->log(
 		'UserID assigned: "%s"',
 			[ 'uid' => $uid ],
@@ -72,7 +72,7 @@ class UserManagement extends Action {
 	 *
 	 * @param array $params
 	 */
-	public function delete(array $params) {
+	public function delete(array $params): void {
 		$this->log(
 			'User deleted: "%s"',
 			$params,
@@ -87,7 +87,7 @@ class UserManagement extends Action {
 	 *
 	 * @param string $uid
 	 */
-	public function unassign(string $uid) {
+	public function unassign(string $uid): void {
 		$this->log(
 			'UserID unassigned: "%s"',
 			[ 'uid' => $uid ],
@@ -100,7 +100,7 @@ class UserManagement extends Action {
 	 *
 	 * @param array $params
 	 */
-	public function change(array $params) {
+	public function change(array $params): void {
 		switch ($params['feature']) {
 			case 'enabled':
 				$this->log(
@@ -130,7 +130,7 @@ class UserManagement extends Action {
 	 *
 	 * @param IUser $user
 	 */
-	public function setPassword(IUser $user) {
+	public function setPassword(IUser $user): void {
 		if ($user->getBackendClassName() === 'Database') {
 			$this->log(
 				'Password of user "%s" has been changed',
diff --git a/apps/admin_audit/lib/Actions/Versions.php b/apps/admin_audit/lib/Actions/Versions.php
index 8594d781d7..6b4badf81b 100644
--- a/apps/admin_audit/lib/Actions/Versions.php
+++ b/apps/admin_audit/lib/Actions/Versions.php
@@ -29,7 +29,7 @@ declare(strict_types=1);
 namespace OCA\AdminAudit\Actions;
 
 class Versions extends Action {
-	public function rollback(array $params) {
+	public function rollback(array $params): void {
 		$this->log('Version "%s" of "%s" was restored.',
 			[
 				'version' => $params['revision'],
@@ -39,7 +39,7 @@ class Versions extends Action {
 		);
 	}
 
-	public function delete(array $params) {
+	public function delete(array $params): void {
 		$this->log('Version "%s" was deleted.',
 			['path' => $params['path']],
 			['path']
diff --git a/apps/admin_audit/lib/AppInfo/Application.php b/apps/admin_audit/lib/AppInfo/Application.php
index 3e67085e3b..d7afb96ea8 100644
--- a/apps/admin_audit/lib/AppInfo/Application.php
+++ b/apps/admin_audit/lib/AppInfo/Application.php
@@ -109,7 +109,7 @@ class Application extends App implements IBootstrap {
 	 * Register hooks in order to log them
 	 */
 	private function registerHooks(LoggerInterface $logger,
-									 IServerContainer $serverContainer) {
+									 IServerContainer $serverContainer): void {
 		$this->userManagementHooks($logger, $serverContainer->get(IUserSession::class));
 		$this->groupHooks($logger, $serverContainer->get(IGroupManager::class));
 		$this->authHooks($logger);
@@ -129,7 +129,7 @@ class Application extends App implements IBootstrap {
 	}
 
 	private function userManagementHooks(LoggerInterface $logger,
-										 IUserSession $userSession) {
+										 IUserSession $userSession): void {
 		$userActions = new UserManagement($logger);
 
 		Util::connectHook('OC_User', 'post_createUser', $userActions, 'create');
@@ -143,7 +143,7 @@ class Application extends App implements IBootstrap {
 	}
 
 	private function groupHooks(LoggerInterface $logger,
-								IGroupManager $groupManager) {
+								IGroupManager $groupManager): void {
 		$groupActions = new GroupManagement($logger);
 
 		assert($groupManager instanceof GroupManager);
@@ -153,7 +153,7 @@ class Application extends App implements IBootstrap {
 		$groupManager->listen('\OC\Group', 'postCreate', [$groupActions, 'createGroup']);
 	}
 
-	private function sharingHooks(LoggerInterface $logger) {
+	private function sharingHooks(LoggerInterface $logger): void {
 		$shareActions = new Sharing($logger);
 
 		Util::connectHook(Share::class, 'post_shared', $shareActions, 'shared');
@@ -165,7 +165,7 @@ class Application extends App implements IBootstrap {
 		Util::connectHook(Share::class, 'share_link_access', $shareActions, 'shareAccessed');
 	}
 
-	private function authHooks(LoggerInterface $logger) {
+	private function authHooks(LoggerInterface $logger): void {
 		$authActions = new Auth($logger);
 
 		Util::connectHook('OC_User', 'pre_login', $authActions, 'loginAttempt');
@@ -174,7 +174,7 @@ class Application extends App implements IBootstrap {
 	}
 
 	private function appHooks(LoggerInterface $logger,
-							  EventDispatcherInterface $eventDispatcher) {
+							  EventDispatcherInterface $eventDispatcher): void {
 		$eventDispatcher->addListener(ManagerEvent::EVENT_APP_ENABLE, function (ManagerEvent $event) use ($logger) {
 			$appActions = new AppManagement($logger);
 			$appActions->enableApp($event->getAppID());
@@ -190,7 +190,7 @@ class Application extends App implements IBootstrap {
 	}
 
 	private function consoleHooks(LoggerInterface $logger,
-								  EventDispatcherInterface $eventDispatcher) {
+								  EventDispatcherInterface $eventDispatcher): void {
 		$eventDispatcher->addListener(ConsoleEvent::EVENT_RUN, function (ConsoleEvent $event) use ($logger) {
 			$appActions = new Console($logger);
 			$appActions->runCommand($event->getArguments());
@@ -198,7 +198,7 @@ class Application extends App implements IBootstrap {
 	}
 
 	private function fileHooks(LoggerInterface $logger,
-							   EventDispatcherInterface $eventDispatcher) {
+							   EventDispatcherInterface $eventDispatcher): void {
 		$fileActions = new Files($logger);
 		$eventDispatcher->addListener(
 			IPreview::EVENT,
@@ -259,20 +259,20 @@ class Application extends App implements IBootstrap {
 		);
 	}
 
-	private function versionsHooks(LoggerInterface $logger) {
+	private function versionsHooks(LoggerInterface $logger): void {
 		$versionsActions = new Versions($logger);
 		Util::connectHook('\OCP\Versions', 'rollback', $versionsActions, 'rollback');
 		Util::connectHook('\OCP\Versions', 'delete', $versionsActions, 'delete');
 	}
 
-	private function trashbinHooks(LoggerInterface $logger) {
+	private function trashbinHooks(LoggerInterface $logger): void {
 		$trashActions = new Trashbin($logger);
 		Util::connectHook('\OCP\Trashbin', 'preDelete', $trashActions, 'delete');
 		Util::connectHook('\OCA\Files_Trashbin\Trashbin', 'post_restore', $trashActions, 'restore');
 	}
 
 	private function securityHooks(LoggerInterface $logger,
-								   EventDispatcherInterface $eventDispatcher) {
+								   EventDispatcherInterface $eventDispatcher): void {
 		$eventDispatcher->addListener(IProvider::EVENT_SUCCESS, function (GenericEvent $event) use ($logger) {
 			$security = new Security($logger);
 			$security->twofactorSuccess($event->getSubject(), $event->getArguments());
diff --git a/apps/admin_audit/lib/BackgroundJobs/Rotate.php b/apps/admin_audit/lib/BackgroundJobs/Rotate.php
index 4244a7e4f9..e0edbc6f4b 100644
--- a/apps/admin_audit/lib/BackgroundJobs/Rotate.php
+++ b/apps/admin_audit/lib/BackgroundJobs/Rotate.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  * @copyright Copyright (c) 2018 Arthur Schiwon <blizzz@arthur-schiwon.de>
  *
diff --git a/apps/admin_audit/tests/Actions/SecurityTest.php b/apps/admin_audit/tests/Actions/SecurityTest.php
index 6a4766fc2e..fab598615b 100644
--- a/apps/admin_audit/tests/Actions/SecurityTest.php
+++ b/apps/admin_audit/tests/Actions/SecurityTest.php
@@ -28,12 +28,12 @@ declare(strict_types=1);
 namespace OCA\AdminAudit\Tests\Actions;
 
 use OCA\AdminAudit\Actions\Security;
-use OCP\ILogger;
 use OCP\IUser;
+use Psr\Log\LoggerInterface;
 use Test\TestCase;
 
 class SecurityTest extends TestCase {
-	/** @var ILogger|\PHPUnit\Framework\MockObject\MockObject */
+	/** @var LoggerInterface|\PHPUnit\Framework\MockObject\MockObject */
 	private $logger;
 
 	/** @var Security */
@@ -45,7 +45,7 @@ class SecurityTest extends TestCase {
 	protected function setUp(): void {
 		parent::setUp();
 
-		$this->logger = $this->createMock(ILogger::class);
+		$this->logger = $this->createMock(LoggerInterface::class);
 		$this->security = new Security($this->logger);
 
 		$this->user = $this->createMock(IUser::class);