diff --git a/lib/GuestManager.php b/lib/GuestManager.php
index c38018a19..a15c849f1 100644
--- a/lib/GuestManager.php
+++ b/lib/GuestManager.php
@@ -77,6 +77,8 @@ public function createGuest(?IUser $createdBy, string $userId, string $email, st
 
 		if ($displayName !== '') {
 			$user->setDisplayName($displayName);
+		} else {
+			$user->setDisplayName($email);
 		}
 
 		if ($language !== '') {