diff --git a/lib/AppInfo/Application.php b/lib/AppInfo/Application.php
index 29b367db7..e8f89e6f7 100644
--- a/lib/AppInfo/Application.php
+++ b/lib/AppInfo/Application.php
@@ -25,6 +25,7 @@ namespace OCA\Deck\AppInfo;
 
 use OCA\Deck\Db\Acl;
 use OCA\Deck\Db\AclMapper;
+use OCA\Deck\Db\AssignedUsersMapper;
 use OCA\Deck\Notification\Notifier;
 use OCP\AppFramework\App;
 use OCA\Deck\Middleware\SharingMiddleware;
@@ -65,12 +66,19 @@ class Application extends App {
 		/** @var IUserManager $userManager */
 		$userManager = $server->getUserManager();
 		$userManager->listen('\OC\User', 'postDelete', function(IUser $user) use ($container) {
+			// delete existing acl entries for deleted user
 			/** @var AclMapper $aclMapper */
 			$aclMapper = $container->query(AclMapper::class);
 			$acls = $aclMapper->findByParticipant(Acl::PERMISSION_TYPE_USER, $user->getUID());
 			foreach ($acls as $acl) {
 				$aclMapper->delete($acl);
 			}
+			// delete existing user assignments
+			$assignmentMapper = $container->query(AssignedUsersMapper::class);
+			$assignments = $assignmentMapper->findByUserId($user->getUID());
+			foreach ($assignments as $assignment) {
+				$assignmentMapper->delete($assignment);
+			}
 		});
 
 		/** @var IUserManager $userManager */
diff --git a/lib/Db/AssignedUsersMapper.php b/lib/Db/AssignedUsersMapper.php
index d2500043c..f1797b0da 100644
--- a/lib/Db/AssignedUsersMapper.php
+++ b/lib/Db/AssignedUsersMapper.php
@@ -50,6 +50,12 @@ class AssignedUsersMapper extends DeckMapper implements IPermissionMapper {
 		return $users;
 	}
 
+	public function findByUserId(string $uid): array {
+		$sql = 'SELECT * FROM `*PREFIX*deck_assigned_users` ' .
+			'WHERE `participant` = ?';
+		return $this->findEntities($sql, [$uid]);
+	}
+
 
 	public function isOwner($userId, $cardId) {
 		return $this->cardMapper->isOwner($userId, $cardId);
diff --git a/lib/Service/BoardService.php b/lib/Service/BoardService.php
index 072f7c1f5..36be5c341 100644
--- a/lib/Service/BoardService.php
+++ b/lib/Service/BoardService.php
@@ -25,6 +25,7 @@ namespace OCA\Deck\Service;
 
 use OCA\Deck\Db\Acl;
 use OCA\Deck\Db\AclMapper;
+use OCA\Deck\Db\AssignedUsersMapper;
 use OCA\Deck\Db\IPermissionMapper;
 use OCA\Deck\Db\Label;
 use OCA\Deck\Notification\NotificationHelper;
@@ -43,6 +44,7 @@ class BoardService {
 	private $l10n;
 	private $permissionService;
 	private $notificationHelper;
+	private $assignedUsersMapper;
 
 	public function __construct(
 		BoardMapper $boardMapper,
@@ -50,7 +52,8 @@ class BoardService {
 		LabelMapper $labelMapper,
 		AclMapper $aclMapper,
 		PermissionService $permissionService,
-		NotificationHelper $notificationHelper
+		NotificationHelper $notificationHelper,
+		AssignedUsersMapper $assignedUsersMapper
 	) {
 		$this->boardMapper = $boardMapper;
 		$this->labelMapper = $labelMapper;
@@ -58,6 +61,7 @@ class BoardService {
 		$this->l10n = $l10n;
 		$this->permissionService = $permissionService;
 		$this->notificationHelper = $notificationHelper;
+		$this->assignedUsersMapper = $assignedUsersMapper;
 	}
 
 	public function findAll($userInfo) {
@@ -243,6 +247,12 @@ class BoardService {
 		/** @var Acl $acl */
 		$acl = $this->aclMapper->find($id);
 		$this->boardMapper->mapAcl($acl);
+		if ($acl->getType() === Acl::PERMISSION_TYPE_USER) {
+			$assignements = $this->assignedUsersMapper->findByUserId($acl->getParticipant());
+			foreach($assignements as $assignement) {
+				$this->assignedUsersMapper->delete($assignement);
+			}
+		}
 		return $this->aclMapper->delete($acl);
 	}