diff --git a/bin/vue-build b/bin/vue-build
index 16919f5fdc..3e786b4a93 100755
--- a/bin/vue-build
+++ b/bin/vue-build
@@ -288,7 +288,7 @@ if (!options.disableWebpackConfig) {
   if (typeof options.webpack === 'object') {
     webpackConfig = webpackMerge.smart(webpackConfig, options.webpack)
   } else if (typeof options.webpack === 'function') {
-    webpackConfig = options.webpack(webpackConfig, options, webpack)
+    webpackConfig = options.webpack(webpackConfig, options, webpack) || webpackConfig
   } else {
     var localWebpackConfigPath = typeof options.webpack === 'string'
       ? cwd(options.webpack)
@@ -313,7 +313,9 @@ try {
 
 checkEntryExists(options.entry)
 
-if (options.watch) {
+if (typeof options.run === 'function') {
+  options.run(webpackConfig, options)
+} else if (options.watch) {
   console.log('> Running in watch mode')
   rm(path.join(options.dist, '*'))
   compiler.watch({}, (err, stats) => handleBuild(err, stats, true))
diff --git a/docs/build.md b/docs/build.md
index c014456c53..ba5c8db811 100644
--- a/docs/build.md
+++ b/docs/build.md
@@ -219,6 +219,29 @@ module.exports = {
 }
 ```
 
+#### run(webpackConfig, options)
+
+Type: `function`
+
+You can use a custom `run` function to perform your own build process instead of the default one. For example, run karma with the processed webpack config:
+
+```js
+const Server = require('karma').Server
+
+module.exports = {
+  run(webpackConfig) {
+    const server = new Server({
+      webpack: webpackConfig,
+      // other karma options...
+    }, exitCode => {
+      console.log('Karma has exited with ' + exitCode)
+      process.exit(exitCode)
+    })
+    server.start()
+  }
+}
+```
+
 ### webpack.config.js
 
 All the webpack options are available here.