diff --git a/lib/modules/CoreDocuments.php b/lib/modules/CoreDocuments.php
index 3f6de68151cb0e1392b1bfd8382e501b4d65e4ac..96afa479dd758e188ac007962faeb85e24d6b6c4 100644
--- a/lib/modules/CoreDocuments.php
+++ b/lib/modules/CoreDocuments.php
@@ -42,6 +42,7 @@ class CoreDocuments extends CorePlugin implements StudipModule, OERModule
             'description' => $material['description']
         ];
         $url = $material->getDownloadUrl();
+        $tmp_name = null;
         if ($url) {
             if ($material['host_id']) {
                 $tmp_name = $GLOBALS['TMP_PATH'] . '/oer_' . $material->getId();