diff --git a/handler/AdminHandler.php b/handler/AdminHandler.php
index f90739f..b48ce46 100644
--- a/handler/AdminHandler.php
+++ b/handler/AdminHandler.php
@@ -340,7 +340,7 @@ class AdminHandler extends request_handler {
         list($md, $title, $use_image_previews, $lang) = input('md, title, b:use_image_previews, lang');
         $lang = PostLanguage::tryFrom($lang);
         if (!$lang)
-            invalid_request();
+            $lang = PostLanguage::getDefault();
         $html = markup::markdownToHtml($md, $use_image_previews, $lang);
         $ctx = skin('admin');
         $html = $ctx->markdownPreview(
diff --git a/htdocs/js/admin/11-write-form.js b/htdocs/js/admin/11-write-form.js
index ff06c3e..ed742b3 100644
--- a/htdocs/js/admin/11-write-form.js
+++ b/htdocs/js/admin/11-write-form.js
@@ -81,11 +81,12 @@ extend(AdminWriteEditForm.prototype, {
             this.previewRequest.abort();
         var params = {
             md: this.form.elements.text.value,
-            use_image_previews: this.isPage() ? 1 : 0,
-            lang: this.getCurrentLang()
+            use_image_previews: this.isPage() ? 1 : 0
         };
-        if (this.isPost())
+        if (this.isPost()) {
             params.title = this.form.elements.title.value;
+            params.lang = this.getCurrentLang();
+        }
         this.previewRequest = ajax.post('/admin/markdown-preview.ajax', params, function(err, response) {
             if (err)
                 return console.error(err);