diff --git a/src/fib.ts b/src/fib.ts
index 8dc8ddd..3d68b3e 100644
--- a/src/fib.ts
+++ b/src/fib.ts
@@ -1,12 +1,15 @@
-// util function that computes the fibonacci numbers
-module.exports = function fibonacci(n) {
-  if (n < 0) {
-    return -1;
-  } else if (n == 0) {
-    return 0;
-  } else if (n == 1) {
-    return 1;
-  }
+// src/fib.ts
+export function fibonacci(n: number): number {
+  if (n < 0) return -1;
+  if (n === 0) return 0;
+  if (n === 1) return 1;
 
-  return fibonacci(n - 1) + fibonacci(n - 2);
-};
+  let a = 0;
+  let b = 1;
+  for (let i = 2; i <= n; i++) {
+    const next = a + b;
+    a = b;
+    b = next;
+  }
+  return b;
+}
\ No newline at end of file
diff --git a/src/fibRoute.ts b/src/fibRoute.ts
index 2d41ca5..e29c157 100644
--- a/src/fibRoute.ts
+++ b/src/fibRoute.ts
@@ -1,16 +1,26 @@
-// Endpoint for querying the fibonacci numbers
+// src/fibRoute.ts
+import type { Request, Response } from "express";
+import { fibonacci } from "./fib";
 
-const fibonacci = require("./fib");
+export default function fibRoute(req: Request, res: Response): void {
+  const numParam: string | undefined = req.params?.num;
 
-export default (req, res) => {
-  const { num } = req.params;
-
-  const fibN = fibonacci(parseInt(num));
-  let result = `fibonacci(${num}) is ${fibN}`;
+  if (typeof numParam !== "string") {
+    res.status(400).send("Missing route parameter 'num'");
+    return;
+  }
 
-  if (fibN < 0) {
-    result = `fibonacci(${num}) is undefined`;
+  const n = Number.parseInt(numParam, 10);
+  if (Number.isNaN(n)) {
+    res.status(400).send(`Invalid number: "${numParam}"`);
+    return;
   }
 
+  const fibN = fibonacci(n);
+  const result =
+    fibN < 0
+      ? `fibonacci(${n}) is undefined`
+      : `fibonacci(${n}) is ${fibN}`;
+
   res.send(result);
-};
+}
\ No newline at end of file