diff --git a/lib/keyboard.class.ts b/lib/keyboard.class.ts
index 0a155c97..b3e92317 100644
--- a/lib/keyboard.class.ts
+++ b/lib/keyboard.class.ts
@@ -4,7 +4,7 @@ import { sleep } from "./sleep.function";
 
 type StringOrKey = string[] | Key[];
 
-const inputIsString = (input: string[] | Key[]): input is string[] => {
+const inputIsString = (input: (string | Key)[]): input is string[] => {
   return input.every((elem: string | Key) => typeof elem === "string");
 };
 
diff --git a/lib/sleep.function.ts b/lib/sleep.function.ts
index 9c067ede..74f9407f 100644
--- a/lib/sleep.function.ts
+++ b/lib/sleep.function.ts
@@ -1,9 +1,9 @@
 export const sleep = async (ms: number) => {
-  return new Promise(resolve => setTimeout(resolve, ms));
+  return new Promise<void>(resolve => setTimeout(resolve, ms));
 };
 
 export const busyWaitForNanoSeconds = (duration: number) => {
-  return new Promise(res => {
+  return new Promise<void>(res => {
     const start = process.hrtime.bigint();
     let isWaiting = true;
     while (isWaiting) {
diff --git a/package-lock.json b/package-lock.json
index 1eff5932..557161b5 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -882,10 +882,9 @@
       }
     },
     "@types/node": {
-      "version": "16.3.2",
-      "resolved": "https://registry.npmjs.org/@types/node/-/node-16.3.2.tgz",
-      "integrity": "sha512-jJs9ErFLP403I+hMLGnqDRWT0RYKSvArxuBVh2veudHV7ifEC1WAmjJADacZ7mRbA2nWgHtn8xyECMAot0SkAw==",
-      "optional": true
+      "version": "16.7.7",
+      "resolved": "https://registry.npmjs.org/@types/node/-/node-16.7.7.tgz",
+      "integrity": "sha512-bxWC4rgIF/FjM7JsPvpk6ZKGITgw27qsYCbi6h4kWZWYpchOLENgvFaRBZUc64Q/M1y+X2EteahRbyo8QFCKdw=="
     },
     "@types/normalize-package-data": {
       "version": "2.4.0",
@@ -7328,9 +7327,9 @@
       }
     },
     "typescript": {
-      "version": "3.8.3",
-      "resolved": "https://registry.npmjs.org/typescript/-/typescript-3.8.3.tgz",
-      "integrity": "sha512-MYlEfn5VrLNsgudQTVJeNaQFUAI7DkhnOjdpAp4T+ku1TfQClewlbSuTVHiA+8skNBgaf02TL/kLOvig4y3G8w==",
+      "version": "4.4.2",
+      "resolved": "https://registry.npmjs.org/typescript/-/typescript-4.4.2.tgz",
+      "integrity": "sha512-gzP+t5W4hdy4c+68bfcv0t400HVJMMd2+H9B7gae1nQlBzCqvrXX+6GL/b3GAgyTH966pzrZ70/fRjwAtZksSQ==",
       "dev": true
     },
     "typical": {
diff --git a/package.json b/package.json
index b9b65235..65d61ea0 100644
--- a/package.json
+++ b/package.json
@@ -68,6 +68,7 @@
   "devDependencies": {
     "@types/clipboardy": "2.0.1",
     "@types/jest": "25.1.4",
+    "@types/node": "16.7.7",
     "istanbul-merge": "1.1.1",
     "jest": "25.1.0",
     "nyc": "15.1.0",
@@ -76,7 +77,7 @@
     "ts-jest": "25.4.0",
     "tslint": "6.1.0",
     "typedoc": "0.17.6",
-    "typescript": "3.8.3",
+    "typescript": "4.4.2",
     "version-bump-prompt": "6.0.2"
   }
 }