diff --git a/cli.js b/cli.js
index cac6b0e..bda9f40 100755
--- a/cli.js
+++ b/cli.js
@@ -1,5 +1,7 @@
 #!/usr/bin/env node
 
+'use strict'
+
 const check = require('./')
 
 const args = require('minimist')(process.argv.slice(2), {
diff --git a/index.js b/index.js
index da68599..7861f38 100644
--- a/index.js
+++ b/index.js
@@ -1,3 +1,5 @@
+'use strict'
+
 const path = require('path')
 const fs = require('fs')
 const readPackage = require('read-package-json')