diff --git a/mod/assign/locallib.php b/mod/assign/locallib.php
index de1b93e216a..8a84c6128b5 100644
--- a/mod/assign/locallib.php
+++ b/mod/assign/locallib.php
@@ -3654,8 +3654,15 @@ class assign {
         $zipwriter = \core_files\archive_writer::get_stream_writer($filename, \core_files\archive_writer::ZIP_WRITER);
 
         // Stream the files into the zip.
-        foreach ($filesforzipping as $pathinzip => $storedfile) {
-            $zipwriter->add_file_from_stored_file($pathinzip, $storedfile);
+        foreach ($filesforzipping as $pathinzip => $file) {
+            if ($file instanceof \stored_file) {
+                // Most of cases are \stored_file.
+                $zipwriter->add_file_from_stored_file($pathinzip, $file);
+            } else if (is_array($file)) {
+                // Save $file as contents, from onlinetext subplugin.
+                $content = reset($file);
+                $zipwriter->add_file_from_string($pathinzip, $content);
+            }
         }
 
         // Finish the archive.