diff --git a/package.json b/package.json
index b108afa..35c8370 100644
--- a/package.json
+++ b/package.json
@@ -21,7 +21,7 @@
     "jest": "^29.3.1",
     "supertest": "^6.3.3",
     "ts-jest": "^29.0.5",
-    "typescript": "^4.9.4"
+    "typescript": "^4.9.5"
   },
   "dependencies": {
     "express": "^4.17.1"
diff --git a/src/fib.ts b/src/fib.ts
index 0d292e9..428270f 100644
--- a/src/fib.ts
+++ b/src/fib.ts
@@ -1,5 +1,5 @@
 // util function that computes the fibonacci numbers
-export default function fibonacci(n) {
+export default function fibonacci(n:number):number {
   if (n < 0) {
     return -1;
   } else if (n == 0) {