diff --git a/tabby-core/src/utils.ts b/tabby-core/src/utils.ts
index 4e7ce896..082bc136 100644
--- a/tabby-core/src/utils.ts
+++ b/tabby-core/src/utils.ts
@@ -67,9 +67,9 @@ export const TAB_COLORS = [
 
 export function serializeFunction <T extends () => Promise<any>> (fn: T): T {
     let queue = Promise.resolve()
-    return (...args) => {
+    return ((...args) => {
         const res = queue.then(() => fn(...args))
         queue = res.catch(() => null)
         return res
-    }
+    }) as T
 }