diff --git a/files/classes/external/stored_file_exporter.php b/files/classes/external/stored_file_exporter.php
index c491170e971..2289beaafcc 100644
--- a/files/classes/external/stored_file_exporter.php
+++ b/files/classes/external/stored_file_exporter.php
@@ -14,15 +14,7 @@
 // You should have received a copy of the GNU General Public License
 // along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
 
-/**
- * Class for exporting stored_file data.
- *
- * @package    core_files
- * @copyright  2015 Frédéric Massart - FMCorz.net
- * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
- */
 namespace core_files\external;
-defined('MOODLE_INTERNAL') || die();
 
 use coding_exception;
 use core_text;
@@ -40,6 +32,9 @@ use stored_file;
  */
 class stored_file_exporter extends \core\external\exporter {
 
+    /** @var int Length of the shortened filename */
+    protected const FILENAMESHORT_LENGTH = 25;
+
     /** @var stored_file */
     protected $file;
 
@@ -142,9 +137,13 @@ class stored_file_exporter extends \core\external\exporter {
     protected function get_other_values(renderer_base $output) {
         $filename = $this->file->get_filename();
         $filenameshort = $filename;
-        if (core_text::strlen($filename) > 25) {
-            $filenameshort = shorten_text(substr($filename, 0, -4), 21, true, '..');
-            $filenameshort .= substr($filename, -4);
+
+        if (core_text::strlen($filename) > static::FILENAMESHORT_LENGTH) {
+            $extension = pathinfo($filename, PATHINFO_EXTENSION);
+            $extensionlength = core_text::strlen($extension) + 1;
+            $filenameshort = core_text::substr($filename, 0, -$extensionlength);
+            $filenameshort = shorten_text($filenameshort, static::FILENAMESHORT_LENGTH - $extensionlength, true, '..') .
+                ".{$extension}";
         }
 
         $icon = $this->file->is_directory() ? file_folder_icon() : file_file_icon($this->file);
diff --git a/files/tests/external/stored_file_exporter_test.php b/files/tests/external/stored_file_exporter_test.php
new file mode 100644
index 00000000000..af7549f8330
--- /dev/null
+++ b/files/tests/external/stored_file_exporter_test.php
@@ -0,0 +1,126 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+namespace core_files\external;
+
+use advanced_testcase;
+use context_user;
+
+/**
+ * Unit tests for stored file exporter
+ *
+ * @package     core_files
+ * @covers      \core_files\external\stored_file_exporter
+ * @copyright   2023 Paul Holden <paulh@moodle.com>
+ * @license     http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class stored_file_exporter_test extends advanced_testcase {
+
+    /**
+     * Test exported data structure
+     */
+    public function test_export(): void {
+        global $PAGE, $USER, $CFG;
+
+        $this->resetAfterTest();
+        $this->setAdminUser();
+
+        $contextuser = context_user::instance($USER->id);
+
+        $file = get_file_storage()->create_file_from_string([
+            'contextid' => $contextuser->id,
+            'userid' => $USER->id,
+            'component' => 'user',
+            'filearea' => 'draft',
+            'itemid' => file_get_unused_draft_itemid(),
+            'filepath' => '/',
+            'filename' => 'Hi.txt',
+        ], 'Hello');
+
+        $exporter = new stored_file_exporter($file, ['context' => $contextuser]);
+        $export = $exporter->export($PAGE->get_renderer('core'));
+
+        $this->assertEquals((object) [
+            'contextid' => $file->get_contextid(),
+            'component' => $file->get_component(),
+            'filearea' => $file->get_filearea(),
+            'itemid' => $file->get_itemid(),
+            'filepath' => $file->get_filepath(),
+            'filename' => $file->get_filename(),
+            'isdir' => false,
+            'isimage' => false,
+            'timemodified' => $file->get_timemodified(),
+            'timecreated' => $file->get_timecreated(),
+            'filesize' => $file->get_filesize(),
+            'author' => $file->get_author(),
+            'license' => $file->get_license(),
+            'filenameshort' => $file->get_filename(),
+            'filesizeformatted' => display_size($file->get_filesize()),
+            'icon' => 'f/text',
+            'timecreatedformatted' => userdate($file->get_timecreated()),
+            'timemodifiedformatted' => userdate($file->get_timemodified()),
+            'url' => "{$CFG->wwwroot}/pluginfile.php/{$contextuser->id}/user/draft/{$file->get_itemid()}/Hi.txt?forcedownload=1",
+        ], $export);
+    }
+
+    /**
+     * Data provider for {@see test_export_filenameshort}
+     *
+     * @return array[]
+     */
+    public static function export_filenameshort_provider(): array {
+        return [
+            // Long filenames (30 characters), with extensions of varying length.
+            ['Lorem ipsum dolor sit amet sit.c', 'Lorem ipsum dolor sit...c'],
+            ['Lorem ipsum dolor sit amet sit.txt', 'Lorem ipsum dolor s...txt'],
+            ['Lorem ipsum dolor sit amet sit.docx', 'Lorem ipsum dolor ...docx'],
+            // Multi-byte filenames.
+            ['Мазитов А.З. практика тусур.py', 'Мазитов А.З. практик...py'],
+        ];
+    }
+
+    /**
+     * Test exporting shortened filename
+     *
+     * @param string $filename
+     * @param string $expected
+     *
+     * @dataProvider export_filenameshort_provider
+     */
+    public function test_export_filenameshort(string $filename, string $expected): void {
+        global $PAGE, $USER;
+
+        $this->resetAfterTest();
+        $this->setAdminUser();
+
+        $contextuser = context_user::instance($USER->id);
+
+        $file = get_file_storage()->create_file_from_string([
+            'contextid' => $contextuser->id,
+            'userid' => $USER->id,
+            'component' => 'user',
+            'filearea' => 'draft',
+            'itemid' => file_get_unused_draft_itemid(),
+            'filepath' => '/',
+            'filename' => $filename,
+        ], 'Hello');
+
+        $exporter = new stored_file_exporter($file, ['context' => $contextuser]);
+        $export = $exporter->export($PAGE->get_renderer('core'));
+
+        $this->assertEquals($expected, $export->filenameshort);
+    }
+}