diff --git a/Classes/Cache/RemoteFileBackend.php b/Classes/Cache/RemoteFileBackend.php
index d3086a20739..a820dd2a1a2 100644
--- a/Classes/Cache/RemoteFileBackend.php
+++ b/Classes/Cache/RemoteFileBackend.php
@@ -105,7 +105,7 @@ public function set($entryIdentifier, $data, array $tags = [], $lifetime = null)
         }
 
         GeneralUtility::writeFile($absoluteCacheDir . $fileName . self::FILE_EXTENSION_TAG, '|' . implode('|', $tags) . '|');
-        GeneralUtility::writeFile($absoluteCacheDir . $fileName . self::FILE_EXTENSION_LIFETIME, $this->calculateExpiryTime($lifetime)->getTimestamp());
+        GeneralUtility::writeFile($absoluteCacheDir . $fileName . self::FILE_EXTENSION_LIFETIME, (string)$this->calculateExpiryTime($lifetime)->getTimestamp());
         GeneralUtility::writeFile($absoluteCacheDir . $fileName . self::FILE_EXTENSION_IDENTIFIER, $entryIdentifier);
     }