diff --git a/code/LeftAndMain.php b/code/LeftAndMain.php
index c95d5df5..6b6c3a33 100644
--- a/code/LeftAndMain.php
+++ b/code/LeftAndMain.php
@@ -99,6 +99,10 @@ class LeftAndMain extends Controller {
 	function init() {
 		parent::init();
 		
+		// The user's theme shouldn't affect the CMS, if, for example, they have replaced
+		// TableListField.ss or Form.ss.
+		SSViewer::set_theme(null);
+		
 		// set language
 		$member = Member::currentUser();
 		if(!empty($member->Locale)) {