diff --git a/lib/private/Files/Cache/Cache.php b/lib/private/Files/Cache/Cache.php
index 9d8e67d1d12..481a384a6e1 100644
--- a/lib/private/Files/Cache/Cache.php
+++ b/lib/private/Files/Cache/Cache.php
@@ -526,7 +526,7 @@ class Cache implements ICache {
 			$this->connection->beginTransaction();
 			if ($sourceData['mimetype'] === 'httpd/unix-directory') {
 				//update all child entries
-				$sourceLength = strlen($sourcePath);
+				$sourceLength = mb_strlen($sourcePath);
 				$query = $this->connection->getQueryBuilder();
 
 				$fun = $query->func();