diff --git a/src/lib/server/db.ts b/src/lib/server/db.ts
index 933149e..c2a140d 100644
--- a/src/lib/server/db.ts
+++ b/src/lib/server/db.ts
@@ -1037,6 +1037,12 @@ function getCachedThumbnail(thumbnailUrl: string): SongThumbnailImage[] | null {
 }
 
 function cacheThumbnail(thumbnailUrl: string, thumbnails: SongThumbnailImage[]) {
+  if (!thumbnails) {
+    // This usually means, that the data is being saved to cached,
+    // while the thumbnail generation is not finished yet
+    logger.debug('will not cache empty thumbnail list', thumbnailUrl);
+    return;
+  }
   const now = new Date().getTime();
   const initialSize = thumbnailCache.size;
   if (initialSize >= maxThumbnailCacheSize) {