diff --git a/lib/setup.php b/lib/setup.php
index 220d3293c3085..d74fe2d2ba79d 100644
--- a/lib/setup.php
+++ b/lib/setup.php
@@ -700,7 +700,7 @@ function stripslashes_deep($value) {
 if (!isset($CFG->themes)) {
     $theme_obj = new stdClass();
     $theme_obj->device = 'default';
-    $theme_obj->theme = 'standardwhite';
+    $theme = $theme_obj->theme = 'standardwhite';
     $current_prefs[] = $theme_obj;
     $CFG->themes = json_encode($current_prefs);
 }
@@ -733,7 +733,7 @@ function stripslashes_deep($value) {
 moodle_setlocale();
 
 if (!empty($CFG->debugvalidators) and !empty($CFG->guestloginbutton)) {
-    if ($theme == 'standardwhite') {    // Temporary measure to help with XHTML validation
+    if (!empty($theme) and $theme == 'standardwhite') {    // Temporary measure to help with XHTML validation
         if (isset($_SERVER['HTTP_USER_AGENT']) and empty($USER->id)) {      // Allow W3CValidator in as user called w3cvalidator (or guest)
             if ((strpos($_SERVER['HTTP_USER_AGENT'], 'W3C_Validator') !== false) or
                 (strpos($_SERVER['HTTP_USER_AGENT'], 'Cynthia') !== false )) {