diff --git a/ftp.js b/ftp.js
index af107f0..5a8960e 100644
--- a/ftp.js
+++ b/ftp.js
@@ -1,3 +1,5 @@
+"use strict";
+
 var util = require('util');
 var JSFtp  = require('jsftp');
 var loop = require('easy-loop');
diff --git a/ftps.js b/ftps.js
index 231dce4..b060104 100644
--- a/ftps.js
+++ b/ftps.js
@@ -1,4 +1,4 @@
-'use strict';
+"use strict";
 var util = require('util');
 var loop = require('easy-loop');
 var EventEmitter = require('events');
diff --git a/lib/file-util.js b/lib/file-util.js
index 95d22cb..827e7dc 100644
--- a/lib/file-util.js
+++ b/lib/file-util.js
@@ -1,3 +1,5 @@
+"use strict";
+
 var fs = require('fs');
 var fse = require('fs-extra');
 var loop = require('easy-loop');
diff --git a/lib/path-util.js b/lib/path-util.js
index a10572e..8a3a22f 100644
--- a/lib/path-util.js
+++ b/lib/path-util.js
@@ -1,3 +1,5 @@
+"use strict";
+
 var path = require('path');
 var o = {};
 module.exports = o;
diff --git a/main.js b/main.js
index 46595ba..ea8e33a 100644
--- a/main.js
+++ b/main.js
@@ -1,4 +1,4 @@
-'use strict';
+"use strict";
 var ftp = require('./ftp');
 var ftps = require('./ftps');