diff --git a/lib/outputrenderers.php b/lib/outputrenderers.php
index b98830b5d3e..bc798b5d91a 100644
--- a/lib/outputrenderers.php
+++ b/lib/outputrenderers.php
@@ -2732,26 +2732,10 @@ class core_renderer extends renderer_base {
     }
 
     /**
-     * Internal implementation of file tree viewer items rendering.
-     *
-     * @param array $dir
-     * @return string
+     * @deprecated since Moodle 4.3
      */
-    public function htmllize_file_tree($dir) {
-        if (empty($dir['subdirs']) and empty($dir['files'])) {
-            return '';
-        }
-        $result = '<ul>';
-        foreach ($dir['subdirs'] as $subdir) {
-            $result .= '<li>'.s($subdir['dirname']).' '.$this->htmllize_file_tree($subdir).'</li>';
-        }
-        foreach ($dir['files'] as $file) {
-            $filename = $file->get_filename();
-            $result .= '<li><span>'.html_writer::link($file->fileurl, $filename).'</span></li>';
-        }
-        $result .= '</ul>';
-
-        return $result;
+    public function htmllize_file_tree() {
+        throw new coding_exception('This function is deprecated and no longer relevant.');
     }
 
     /**
@@ -5629,17 +5613,6 @@ class core_renderer_maintenance extends core_renderer {
         return '';
     }
 
-    /**
-     * Does nothing. The maintenance renderer cannot produce and HTML file tree.
-     *
-     * @param array $dir
-     * @return string
-     */
-    public function htmllize_file_tree($dir) {
-        return '';
-
-    }
-
     /**
      * Overridden confirm message for upgrades.
      *
diff --git a/theme/upgrade.txt b/theme/upgrade.txt
index 5f59249af99..e5e41b056a7 100644
--- a/theme/upgrade.txt
+++ b/theme/upgrade.txt
@@ -1,6 +1,9 @@
 This files describes API changes in /theme/* themes,
 information provided here is intended especially for theme designer.
 
+=== 4.3 ===
+* The core_renderer::htmllize_file_tree method has been deprecated. This was missed before Moodle 2.0.
+
 === 4.2 ===
 * The moodle-core-popuphelp YUI modal has been removed. It has not been actively used in Moodle since 3.3. It should be replaced with appropriate ESM/AMD JavaScript.
 * The moodle-core-tooltip YUI modal has been removed. It should be replaced with appropriate ESM/AMD JavaScript.