diff --git a/lib/index.js b/lib/index.js
index 47ff6b49..278cbbea 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -11,6 +11,7 @@ var async       = require("async")
 var connect     = require("connect")
 var middleware  = require("./middleware")
 var mime        = require('mime')
+var tmp         = require("os").tmpdir()
 
 
 /**
@@ -160,17 +161,37 @@ exports.compile = function(projectPath, outputPath, callback){
     outputPath = "www"
   }
 
+  // harp will write the project out here first, and if successul, it'll get
+  // moved across to the real outputPath - to allow for compile to fail, without
+  // blowing away the previous version.
+  var tmpOutputPath = path.join(tmp, "www" + (Math.random() * 1000 | 0))
+  outputPath = path.resolve(projectPath, outputPath)
+
+  // if the compile was successful, move across the outputPath then call callback
+  var complete = function (err, config) {
+    if (!err) {
+      fs.copy(tmpOutputPath, outputPath, function () {
+        fs.remove(tmpOutputPath, function () {
+          callback(err, config)
+        })
+      })
+    } else {
+      // blow away the old directory
+      fs.remove(tmpOutputPath, function () {
+        callback(err, config)
+      })
+    }
+  }
 
   /**
    * Setup all the paths and collect all the data
    */
 
   try{
-    outputPath = path.resolve(projectPath, outputPath)
     var setup  = helpers.setup(projectPath, "production")
     var poly   = polymer.root(setup.publicPath, setup.config.globals)
   }catch(err){
-    return callback(err)
+    return complete(err)
   }
 
 
@@ -180,7 +201,7 @@ exports.compile = function(projectPath, outputPath, callback){
    */
 
   if(!helpers.willAllow(projectPath, outputPath)){
-    return callback({
+    return complete({
       type: "Invalid Output Path",
       message: "Output path cannot be greater then one level up from project path and must be in directory starting with `_` (underscore).",
       projectPath: projectPath,
@@ -199,7 +220,7 @@ exports.compile = function(projectPath, outputPath, callback){
         done(error)
       }else{
         if(body){
-          var dest = path.resolve(outputPath, polymer.helpers.outputPath(file))
+          var dest = path.resolve(tmpOutputPath, polymer.helpers.outputPath(file))
           fs.mkdirp(path.dirname(dest), function(err){
             fs.writeFile(dest, body, done)
           })
@@ -220,7 +241,7 @@ exports.compile = function(projectPath, outputPath, callback){
   var copyFile = function(file, done){
     var ext = path.extname(file)
     if(!polymer.helpers.shouldIgnore(file) && [".jade", ".ejs", ".md", ".styl", ".less", ".scss", ".coffee"].indexOf(ext) === -1){
-      var localPath = path.resolve(outputPath, file)
+      var localPath = path.resolve(tmpOutputPath, file)
       fs.mkdirp(path.dirname(localPath), function(err){
         fs.copy(path.resolve(setup.publicPath, file), localPath, done)
       })
@@ -233,18 +254,18 @@ exports.compile = function(projectPath, outputPath, callback){
    * Scan dir, Compile Less and Jade, Copy the others
    */
 
-  helpers.prime(outputPath, { ignore: projectPath }, function(err){
+  helpers.prime(tmpOutputPath, { ignore: projectPath }, function(err){
     if(err) console.log(err)
 
     helpers.ls(setup.publicPath, function(err, results){
       async.eachLimit(results, 72, compileFile, function(err){
         if(err){
-          callback(err)
+          complete(err)
         }else{
           async.eachLimit(results, 72, copyFile, function(err){
             setup.config['harp_version'] = pkg.version
             delete setup.config.globals
-            callback(null, setup.config)
+            complete(null, setup.config)
           })
         }
       })