diff --git a/lib/private/preview.php b/lib/private/preview.php
index ba2cbd33bf39e60ee4a6bd1f51b7ab01d0648a7a..d6bff961a7334de15c69deb8a4f63f6151973984 100755
--- a/lib/private/preview.php
+++ b/lib/private/preview.php
@@ -808,6 +808,10 @@ class Preview {
 	}
 
 
+	/**
+	 * @param int $fileId
+	 * @return string
+	 */
 	private function getPreviewPath($fileId) {
 		return $this->getThumbnailsFolder() . '/' . $fileId . '/';
 	}