diff --git a/frontend/src/data/service/MangaUpdatesDataService.ts b/frontend/src/data/service/MangaUpdatesDataService.ts
index 20ae4e4..d4b1505 100644
--- a/frontend/src/data/service/MangaUpdatesDataService.ts
+++ b/frontend/src/data/service/MangaUpdatesDataService.ts
@@ -137,7 +137,7 @@ export default class MangaUpdatesDataService {
             const chapter = parseInt(match[1]);
             return r.groups.map(g => ({series_id: s.series_id, group: g.name, chapter: chapter} as MangaUpdatesChapter));
           })
-          .flat();
+          .flat() as MangaUpdatesChapter[];
 
         //only keep chapter with the highest chapter number per group
         const filtered = Array.from(groupBy(updates, c => c.group).values())
diff --git a/frontend/src/util.ts b/frontend/src/util.ts
index f5ab148..a78ab75 100644
--- a/frontend/src/util.ts
+++ b/frontend/src/util.ts
@@ -1,4 +1,4 @@
-export default function groupBy<K, V>(arr: V[], fn: (v: V) => K): Map<K, V[]> {
+export default function groupBy<K, V>(arr: V[], fn: (value: V) => K): Map<K, V[]> {
   const map = new Map<K, V[]>();
   arr.forEach(e => {
     const key = fn(e);