diff --git a/src/Forms/HTMLEditor/HTMLEditorConfig.php b/src/Forms/HTMLEditor/HTMLEditorConfig.php
index df863b78b..35508d4b6 100644
--- a/src/Forms/HTMLEditor/HTMLEditorConfig.php
+++ b/src/Forms/HTMLEditor/HTMLEditorConfig.php
@@ -51,6 +51,11 @@ abstract class HTMLEditorConfig
      */
     private static $default_config = 'default';
 
+    /**
+     * @var List of themes defined for the frontend
+     */
+    private static $user_themes = [];
+
     /**
      * Get the HTMLEditorConfig object for the given identifier. This is a correct way to get an HTMLEditorConfig
      * instance - do not call 'new'
@@ -147,6 +152,15 @@ abstract class HTMLEditorConfig
         return $configs;
     }
 
+    /**
+     * Set user defined (non-admin) themes
+     * @param array $themes
+     */
+    public static function set_user_themes($themes)
+    {
+        self::config()->set('user_themes', $themes);
+    }
+
     /**
      * Get the current value of an option
      *
diff --git a/src/Forms/HTMLEditor/TinyMCEConfig.php b/src/Forms/HTMLEditor/TinyMCEConfig.php
index 79189c8ba..c62a5adb4 100644
--- a/src/Forms/HTMLEditor/TinyMCEConfig.php
+++ b/src/Forms/HTMLEditor/TinyMCEConfig.php
@@ -616,9 +616,8 @@ class TinyMCEConfig extends HTMLEditorConfig
 
         // Add standard editor.css
         $editor[] = $this->getAdminModule()->getResourceURL('client/dist/styles/editor.css');
-
         // Themed editor.css
-        $themedEditor = ThemeResourceLoader::inst()->findThemedCSS('editor', SSViewer::get_themes());
+        $themedEditor = ThemeResourceLoader::inst()->findThemedCSS('editor', $this->config()->user_themes);
         if ($themedEditor) {
             $editor[] = Director::absoluteURL($themedEditor, Director::BASE);
         }