diff --git a/app/javascript/mastodon/features/ui/components/sign_in_banner.jsx b/app/javascript/mastodon/features/ui/components/sign_in_banner.jsx
index 25de95fd37..e54144b074 100644
--- a/app/javascript/mastodon/features/ui/components/sign_in_banner.jsx
+++ b/app/javascript/mastodon/features/ui/components/sign_in_banner.jsx
@@ -17,7 +17,7 @@ const SignInBanner = () => {
 
   let signupButton;
 
-  const signupUrl = useAppSelector((state) => state.getIn(['server', 'server', 'registrations', 'url'], '/auth/sign_up'));
+  const signupUrl = useAppSelector((state) => state.getIn(['server', 'server', 'registrations', 'url'], '/auth/sign_up') || '/auth/sign_up');
 
   if (registrationsOpen) {
     signupButton = (