diff --git a/lib/utils/array.js b/lib/utils/array.js
deleted file mode 100644
index fb9cff07..00000000
--- a/lib/utils/array.js
+++ /dev/null
@@ -1,3 +0,0 @@
-export default function last(arr) {
-  return arr[arr.length - 1];
-}
diff --git a/lib/utils/array.ts b/lib/utils/array.ts
new file mode 100644
index 00000000..b9475300
--- /dev/null
+++ b/lib/utils/array.ts
@@ -0,0 +1,3 @@
+export default function last<T>(arr: T[]): T {
+  return arr[arr.length - 1];
+}
diff --git a/lib/utils/file.js b/lib/utils/file.ts
similarity index 84%
rename from lib/utils/file.js
rename to lib/utils/file.ts
index 702c5224..f2b96a38 100644
--- a/lib/utils/file.js
+++ b/lib/utils/file.ts
@@ -10,7 +10,9 @@
  * PR: https://github.com/kevva/executable/pull/10
  */
 
-export default function isExecutable(fileStat) {
+import { Stats } from "fs";
+
+export default function isExecutable(fileStat: Stats): boolean {
   if (process.platform === 'win32') {
     return true;
   }