diff --git a/.eslintrc.json b/.eslintrc.json
index 6451d8e3..845527f8 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -45,6 +45,7 @@
     "semi": ["warn", "always"],
     "space-before-blocks": ["warn", "always"],
     "space-before-function-paren": ["warn", "never"],
-    "space-in-parens": ["warn", "never"]
+    "space-in-parens": ["warn", "never"],
+    "strict": ["warn", "global"]
   }
 }
diff --git a/cli.js b/cli.js
index de750cff..2019d5ff 100644
--- a/cli.js
+++ b/cli.js
@@ -1,5 +1,7 @@
 #!/usr/bin/env node
 
+'use strict';
+
 var mime = require('./mime.js');
 var file = process.argv[2];
 var type = mime.getType(file);
diff --git a/index.js b/index.js
index 43a400d2..c816606a 100644
--- a/index.js
+++ b/index.js
@@ -1,2 +1,4 @@
+'use strict';
+
 const Mime = require('./Mime');
 module.exports = new Mime(require('./types/standard'), require('./types/other'));
diff --git a/lite.js b/lite.js
index 275b216d..6f910c90 100644
--- a/lite.js
+++ b/lite.js
@@ -1,2 +1,4 @@
+'use strict';
+
 const Mime = require('./Mime');
 module.exports = new Mime(require('./types/standard'));
diff --git a/src/build.js b/src/build.js
index ae773d3f..aad81441 100755
--- a/src/build.js
+++ b/src/build.js
@@ -1,5 +1,7 @@
 #!/usr/bin/env node
 
+'use strict';
+
 const fs = require('fs');
 const path = require('path');
 
diff --git a/src/test.js b/src/test.js
index ca5f9375..0112b9f7 100644
--- a/src/test.js
+++ b/src/test.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var mime = require('..');
 var mimeTypes = require('../node_modules/mime-types');
 var assert = require('assert');