diff --git a/index.js b/index.js
index d1ec474..98bcd0f 100644
--- a/index.js
+++ b/index.js
@@ -5,11 +5,12 @@ const through = require('through2')
 module.exports = function (fn) {
     return through.obj(function (file, enc, cb) {
         const contents = fn(String(file.contents), file.path, file) || file.contents
+        const modifiedFile = file.clone()
 
         if (file.isBuffer() === true) {
-            file.contents = new Buffer(contents)
+            modifiedFile.contents = new Buffer(contents)
         }
 
-        cb(null, file)
+        cb(null, modifiedFile)
     })
-}
\ No newline at end of file
+}