diff --git a/web/src/util.ts b/web/src/util.ts
index 11003be..ec7c78c 100644
--- a/web/src/util.ts
+++ b/web/src/util.ts
@@ -228,7 +228,8 @@ async function share(title: string, url: string, btn?: HTMLElement){
 function toast(msg: string, bad?: boolean){
   const t=document.createElement('div'), box=$('#toasts');
   t.className='toast'+(bad?' bad':''); t.textContent=msg;
-  if(bad) haptic('warn');
+  // haptic is native.ts's, which the admin page's script is not built from (#436).
+  if(bad && typeof haptic==='function') haptic('warn');
   const go=()=>{t.style.opacity='0';t.style.transition='opacity .3s';setTimeout(()=>t.remove(),320)};
   // An error stays until it is put away: gone after six seconds, it was easy to miss and could not
   // be read again (#303).