diff --git a/index.js b/index.js
index ec54c96..b63d98b 100644
--- a/index.js
+++ b/index.js
@@ -2,6 +2,7 @@ var crypto = require('crypto')
 var fs = require('fs')
 var zlib = require('zlib')
 var path = require('path')
+var path = require('path')
 var mime = require('mime-types')
 var compressible = require('compressible')
 var readDir = require('fs-readdir-recursive')
@@ -15,7 +16,7 @@ module.exports = function staticCache(dir, options, files) {
   }
 
   options = options || {}
-  options.prefix = (options.prefix || '').replace(/\/$/, '') + '/'
+  options.prefix = (options.prefix || '').replace(/\/$/, '') + path.sep
   files = files || options.files || Object.create(null)
   dir = dir || options.dir || process.cwd()
   var enableGzip = !!options.gzip