diff --git a/src/components/common/SelectSinger.tsx b/src/components/common/SelectSinger.tsx
index 648b93a..e193e88 100644
--- a/src/components/common/SelectSinger.tsx
+++ b/src/components/common/SelectSinger.tsx
@@ -49,7 +49,7 @@ const SelectSinger: React.FC<SelectSingerProps> = ({ isOpen, onClose, song }) =>
         order: nextOrder,
         singer: {
           name: singer.name,
-          lastLogin: singer.lastLogin,
+          lastLogin: singer.lastLogin || '',
         },
         song: song,
       };
diff --git a/src/firebase/services.ts b/src/firebase/services.ts
index f1ff241..4cb64a2 100644
--- a/src/firebase/services.ts
+++ b/src/firebase/services.ts
@@ -236,7 +236,7 @@ export const singerService = {
     
     // Check if singer already exists
     const existingSinger = Object.values(currentSingers).find((singer) => 
-      (singer as Singer).name.toLowerCase() === singerName.toLowerCase()
+      (String((singer as Singer).name || '').toLowerCase() === String(singerName || '').toLowerCase())
     );
     
     if (existingSinger) {