diff --git a/lib/middleware/karma.js b/lib/middleware/karma.js
index 2e603b382..0c965a521 100644
--- a/lib/middleware/karma.js
+++ b/lib/middleware/karma.js
@@ -15,6 +15,8 @@ var path = require('path')
 var util = require('util')
 var url = require('url')
 
+var log = require('../logger').create('middleware:karma')
+
 var urlparse = function (urlStr) {
   var urlObj = url.parse(urlStr, true)
   urlObj.query = urlObj.query || {}
@@ -59,10 +61,20 @@ var getXUACompatibleUrl = function (url) {
   return value
 }
 
-var createKarmaMiddleware = function (filesPromise, serveStaticFile, serveFile,
-  /* config.basePath */ basePath, /* config.urlRoot */ urlRoot, /* config.client */ client,
-  /* config.customContextFile */ customContextFile, /* config.customDebugFile */ customDebugFile) {
+var createKarmaMiddleware = function (
+  filesPromise,
+  serveStaticFile,
+  serveFile,
+  injector,
+  /* config.basePath */ basePath,
+  /* config.urlRoot */ urlRoot
+) {
   return function (request, response, next) {
+    // These config values should be up to date on every request
+    var client = injector.get('config.client')
+    var customContextFile = injector.get('config.customContextFile')
+    var customDebugFile = injector.get('config.customDebugFile')
+
     var requestUrl = request.normalizedUrl.replace(/\?.*/, '')
 
     // redirect /__karma__ to /__karma__ (trailing slash)
@@ -110,13 +122,17 @@ var createKarmaMiddleware = function (filesPromise, serveStaticFile, serveFile,
       return filesPromise.then(function (files) {
         var fileServer
         var requestedFileUrl
+        log.debug('custom files', customContextFile, customDebugFile)
         if (isRequestingContextFile && customContextFile) {
+          log.debug('Serving customContextFile %s', customContextFile)
           fileServer = serveFile
           requestedFileUrl = customContextFile
         } else if (isRequestingDebugFile && customDebugFile) {
+          log.debug('Serving customDebugFile %s', customDebugFile)
           fileServer = serveFile
           requestedFileUrl = customDebugFile
         } else {
+          log.debug('Serving static request %s', requestUrl)
           fileServer = serveStaticFile
           requestedFileUrl = requestUrl
         }
@@ -197,9 +213,5 @@ var createKarmaMiddleware = function (filesPromise, serveStaticFile, serveFile,
   }
 }
 
-createKarmaMiddleware.$inject = ['filesPromise', 'serveStaticFile', 'serveFile',
-  'config.basePath', 'config.urlRoot', 'config.client', 'config.customContextFile',
-  'config.customDebugFile']
-
 // PUBLIC API
 exports.create = createKarmaMiddleware
diff --git a/lib/web-server.js b/lib/web-server.js
index dc200fda6..1405032c0 100644
--- a/lib/web-server.js
+++ b/lib/web-server.js
@@ -55,6 +55,7 @@ var createWebServer = function (injector, emitter, fileList) {
 
   var proxyMiddlewareInstance = injector.invoke(proxyMiddleware.create)
 
+  log.debug('Instantiating middleware')
   var handler = connect()
     .use(injector.invoke(runnerMiddleware.create))
     .use(injector.invoke(stopperMiddleware.create))
diff --git a/test/unit/middleware/karma.spec.js b/test/unit/middleware/karma.spec.js
index 534a33453..ef78829cb 100644
--- a/test/unit/middleware/karma.spec.js
+++ b/test/unit/middleware/karma.spec.js
@@ -34,13 +34,31 @@ describe('middleware.karma', () => {
 
   var handler = serveFile = filesDeferred = nextSpy = response = null
 
+  var clientConfig = {foo: 'bar'}
+  var injector = {
+    get (val) {
+      switch (val) {
+        case 'config.client':
+          return clientConfig
+        default:
+          return null
+      }
+    }
+  }
+
   beforeEach(() => {
-    var clientConfig = {foo: 'bar'}
     nextSpy = sinon.spy()
     response = new HttpResponseMock()
     filesDeferred = helper.defer()
     serveFile = createServeFile(fsMock, '/karma/static')
-    handler = createKarmaMiddleware(filesDeferred.promise, serveFile, null, '/base/path', '/__karma__/', clientConfig)
+    handler = createKarmaMiddleware(
+      filesDeferred.promise,
+      serveFile,
+      null,
+      injector,
+      '/base/path',
+      '/__karma__/'
+    )
   })
 
   // helpers
@@ -92,7 +110,14 @@ describe('middleware.karma', () => {
   })
 
   it('should serve client.html', (done) => {
-    handler = createKarmaMiddleware(null, serveFile, null, '/base', '/')
+    handler = createKarmaMiddleware(
+      null,
+      serveFile,
+      null,
+      injector,
+      '/base',
+      '/'
+    )
 
     response.once('end', () => {
       expect(nextSpy).not.to.have.been.called
@@ -104,7 +129,14 @@ describe('middleware.karma', () => {
   })
 
   it('should serve /?id=xxx', (done) => {
-    handler = createKarmaMiddleware(null, serveFile, null, '/base', '/')
+    handler = createKarmaMiddleware(
+      null,
+      serveFile,
+      null,
+      injector,
+      '/base',
+      '/'
+    )
 
     response.once('end', () => {
       expect(nextSpy).not.to.have.been.called
@@ -116,7 +148,14 @@ describe('middleware.karma', () => {
   })
 
   it('should serve /?x-ua-compatible with replaced values', (done) => {
-    handler = createKarmaMiddleware(null, serveFile, null, '/base', '/')
+    handler = createKarmaMiddleware(
+      null,
+      serveFile,
+      null,
+      injector,
+      '/base',
+      '/'
+    )
 
     response.once('end', () => {
       expect(nextSpy).not.to.have.been.called
@@ -351,4 +390,47 @@ describe('middleware.karma', () => {
       done()
     })
   })
+
+  it('should update handle updated configs', (done) => {
+    let i = 0
+    handler = createKarmaMiddleware(
+      filesDeferred.promise,
+      serveFile,
+      null,
+      {
+        get (val) {
+          if (val === 'config.client') {
+            i++
+            if (i === 1) {
+              return {foo: 'bar'}
+            } else {
+              return {foo: 'baz'}
+            }
+          } else {
+            return null
+          }
+        }
+      },
+      '/base/path',
+      '/__karma__/'
+    )
+
+    includedFiles([
+      new MockFile('/first.js')
+    ])
+    fsMock._touchFile('/karma/static/debug.html', 1, '%CLIENT_CONFIG%')
+
+    response.once('end', () => {
+      expect(response).to.beServedAs(200, 'window.__karma__.config = {"foo":"bar"};\n')
+
+      response = new HttpResponseMock()
+      callHandlerWith('/__karma__/debug.html')
+      response.once('end', () => {
+        expect(response).to.beServedAs(200, 'window.__karma__.config = {"foo":"baz"};\n')
+        done()
+      })
+    })
+
+    callHandlerWith('/__karma__/debug.html')
+  })
 })