diff --git a/login/index.php b/login/index.php
index 25312086d8a..ca9ddc994db 100644
--- a/login/index.php
+++ b/login/index.php
@@ -314,7 +314,7 @@ if (!empty($CFG->alternateloginurl)) {
 
     $loginurlstr = $loginurl->out(false);
 
-    if (strpos($SESSION->wantsurl, $loginurlstr) === 0) {
+    if (strpos($SESSION->wantsurl ?? '', $loginurlstr) === 0) {
         // We do not want to return to alternate url.
         $SESSION->wantsurl = null;
     }