diff --git a/apps/dav/lib/CardDAV/SyncService.php b/apps/dav/lib/CardDAV/SyncService.php
index 365b5c16f8c5e..a3d6b94f9ef20 100644
--- a/apps/dav/lib/CardDAV/SyncService.php
+++ b/apps/dav/lib/CardDAV/SyncService.php
@@ -156,7 +156,7 @@ private function buildSyncCollectionRequestBody(?string $syncToken): string {
 		$dom = new \DOMDocument('1.0', 'UTF-8');
 		$dom->formatOutput = true;
 		$root = $dom->createElementNS('DAV:', 'd:sync-collection');
-		$sync = $dom->createElement('d:sync-token', $syncToken);
+		$sync = $dom->createElement('d:sync-token', $syncToken ?? '');
 		$prop = $dom->createElement('d:prop');
 		$cont = $dom->createElement('d:getcontenttype');
 		$etag = $dom->createElement('d:getetag');