diff --git a/index.js b/index.js
index 73058aa..5e6c871 100644
--- a/index.js
+++ b/index.js
@@ -1,14 +1,19 @@
-var gutil = require("gulp-util");
-var through = require("through2");
-var assign = require("object-assign");
-var path  = require('path');
-var sass = require("node-sass");
+var gutil = require('gulp-util');
+var through = require('through2');
+var assign = require('object-assign');
+var path = require('path');
+var sass = require('node-sass');
 var applySourceMap = require('vinyl-sourcemaps-apply');
 
 var PLUGIN_NAME = 'gulp-sass';
 
 module.exports = function(options) {
+  'use strict';
+
   return through.obj(function(file, enc, cb) {
+    var opts,
+        callback;
+
     if (file.isNull()) {
       return cb(null, file);
     }
@@ -19,7 +24,7 @@ module.exports = function(options) {
       return cb();
     }
 
-    var opts = assign({}, options);
+    opts = assign({}, options);
     opts.file = file.path;
 
     // Generate Source Maps if plugin source-map present
@@ -28,7 +33,7 @@ module.exports = function(options) {
       opts.omitSourceMapUrl = true;
     }
 
-    var callback = function(error, obj) {
+    callback = function(error, obj) {
       if (error) {
         return cb(new gutil.PluginError(
           PLUGIN_NAME, error.message + ' on line ' + error.line + ' in ' + error.file