diff --git a/mod/assign/locallib.php b/mod/assign/locallib.php
index 825b7087361..ce652aa9933 100644
--- a/mod/assign/locallib.php
+++ b/mod/assign/locallib.php
@@ -2505,27 +2505,6 @@ class assign {
         return $useridlist;
     }
 
-    /**
-     * Generate zip file from array of given files.
-     *
-     * @param array $filesforzipping - array of files to pass into archive_to_pathname.
-     *                                 This array is indexed by the final file name and each
-     *                                 element in the array is an instance of a stored_file object.
-     * @return path of temp file - note this returned file does
-     *         not have a .zip extension - it is a temp file.
-     */
-    protected function pack_files($filesforzipping) {
-        global $CFG;
-        // Create path for new zip file.
-        $tempzip = tempnam($CFG->tempdir . '/', 'assignment_');
-        // Zip files.
-        $zipper = new zip_packer();
-        if ($zipper->archive_to_pathname($filesforzipping, $tempzip)) {
-            return $tempzip;
-        }
-        return false;
-    }
-
     /**
      * Finds all assignment notifications that have yet to be mailed out, and mails them.
      *
@@ -3660,13 +3639,26 @@ class assign {
                                                                     'action'=>'grading'));
             $result .= $this->get_renderer()->continue_button($url);
             $result .= $this->view_footer();
-        } else if ($zipfile = $this->pack_files($filesforzipping)) {
-            \mod_assign\event\all_submissions_downloaded::create_from_assign($this)->trigger();
-            // Send file and delete after sending.
-            send_temp_file($zipfile, $filename);
-            // We will not get here - send_temp_file calls exit.
+
+            return $result;
         }
-        return $result;
+
+        // Log zip as downloaded.
+        \mod_assign\event\all_submissions_downloaded::create_from_assign($this)->trigger();
+
+        // Close the session.
+        \core\session\manager::write_close();
+
+        $zipwriter = \core_files\archive_writer::get_stream_writer($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);
+        }
+
+        // Finish the archive.
+        $zipwriter->finish();
+        exit();
     }
 
     /**