diff --git a/typo3/sysext/frontend/Classes/Resource/FileCollector.php b/typo3/sysext/frontend/Classes/Resource/FileCollector.php
index 4533b501da6b22742aff0d090ff8406014863407..41d5dc7930484f2b12c57528af5984ec4e132bbe 100644
--- a/typo3/sysext/frontend/Classes/Resource/FileCollector.php
+++ b/typo3/sysext/frontend/Classes/Resource/FileCollector.php
@@ -203,7 +203,7 @@ class FileCollector implements \Countable, LoggerAwareInterface
                     FileInterface $b
                 ) use ($sortingProperty) {
                     if ($a->hasProperty($sortingProperty) && $b->hasProperty($sortingProperty)) {
-                        return strnatcasecmp($a->getProperty($sortingProperty), $b->getProperty($sortingProperty));
+                        return strnatcasecmp((string)$a->getProperty($sortingProperty), (string)$b->getProperty($sortingProperty));
                     }
                     return 0;
                 }