diff --git a/lib/private/Repair/Owncloud/SaveAccountsTableData.php b/lib/private/Repair/Owncloud/SaveAccountsTableData.php
index 8d6e2e71b54..e934dda5e8b 100644
--- a/lib/private/Repair/Owncloud/SaveAccountsTableData.php
+++ b/lib/private/Repair/Owncloud/SaveAccountsTableData.php
@@ -173,7 +173,7 @@ class SaveAccountsTableData implements IRepairStep {
 
 		if ($userdata['display_name'] !== null) {
 			// user.displayname only allows 64 characters but old accounts.display_name allowed 255 characters
-			$update->setParameter('displayname', substr($userdata['display_name'], 0, 64))
+			$update->setParameter('displayname', mb_substr($userdata['display_name'], 0, 64))
 				->setParameter('userid', $userdata['user_id']);
 			$update->execute();
 		}