diff --git a/hexdump.js b/hexdump.js
index 2eec2e4..0ac08ce 100644
--- a/hexdump.js
+++ b/hexdump.js
@@ -1,3 +1,5 @@
+'use strict'
+
 const wout = (s) => {
   process.stdout.write(s)
 }