diff --git a/package.json b/package.json
index a1fa7cb..20db1dc 100644
--- a/package.json
+++ b/package.json
@@ -86,7 +86,7 @@
     "prettier": "^2.1.2",
     "rimraf": "^3.0.0",
     "ts-jest": "^25.2.1",
-    "typescript": "^3.4.5"
+    "typescript": "^4.1.2"
   },
   "resolutions": {
     "@types/react": "^16.x"
diff --git a/src/utils.ts b/src/utils.ts
index 16df683..c79c8b8 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -82,7 +82,7 @@ export function validateExportLifecycle(exports: any) {
 class Deferred<T> {
   promise: Promise<T>;
 
-  resolve!: (value?: T | PromiseLike<T>) => void;
+  resolve!: (value: T | PromiseLike<T>) => void;
 
   reject!: (reason?: any) => void;