diff --git a/lib/cli.js b/lib/cli.js
index f652af284..b7dd8f446 100644
--- a/lib/cli.js
+++ b/lib/cli.js
@@ -38,7 +38,16 @@ var processArgs = function (argv, options, fs, path) {
   }
 
   if (helper.isString(options.logLevel)) {
-    options.logLevel = constant['LOG_' + options.logLevel.toUpperCase()] || constant.LOG_DISABLE
+    var logConstant = constant['LOG_' + options.logLevel.toUpperCase()]
+    if (helper.isDefined(logConstant)) {
+      options.logLevel = logConstant
+    } else {
+      console.error('Log level must be one of disable, error, warn, info, or debug.')
+      process.exit(1)
+    }
+  } else if (helper.isDefined(options.logLevel)) {
+    console.error('Log level must be one of disable, error, warn, info, or debug.')
+    process.exit(1)
   }
 
   if (helper.isString(options.singleRun)) {
diff --git a/test/unit/cli.spec.coffee b/test/unit/cli.spec.coffee
index e84952487..dc4413f76 100644
--- a/test/unit/cli.spec.coffee
+++ b/test/unit/cli.spec.coffee
@@ -8,6 +8,8 @@ describe 'cli', ->
   constant = require '../../lib/constants'
   path = require 'path'
   mocks = require 'mocks'
+  loadFile = mocks.loadFile
+  mockery = m = e = null
 
   fsMock = mocks.fs.create
     cwd:
@@ -26,9 +28,26 @@ describe 'cli', ->
 
   processArgs = (args, opts) ->
     argv = optimist.parse(args)
-    cli.processArgs argv, opts || {}, fsMock, pathMock
-
-  beforeEach -> setCWD '/'
+    e.processArgs argv, opts || {}, fsMock, pathMock
+
+  beforeEach ->
+    setCWD '/'
+    mockery = {}
+    mockery.process = exit: sinon.spy()
+    mockery.console = error: sinon.spy()
+
+    # load file under test
+    m = loadFile __dirname + '/../../lib/cli.js', mockery, {
+      global: {},
+      console: mockery.console,
+      process: mockery.process,
+      require: (path) ->
+        if path.indexOf('./') is 0
+          require '../../lib/' + path
+        else
+          require path
+    }
+    e = m.exports
 
   describe 'processArgs', ->
 
@@ -95,6 +114,12 @@ describe 'cli', ->
       options = processArgs ['--log-level', 'warn']
       expect(options.logLevel).to.equal constant.LOG_WARN
 
+      options = processArgs ['--log-level', 'foo']
+      expect(mockery.process.exit).to.have.been.calledWith 1
+
+      options = processArgs ['--log-level']
+      expect(mockery.process.exit).to.have.been.calledWith 1
+
 
     it 'should parse browsers into an array', ->
       options = processArgs ['--browsers', 'Chrome,ChromeCanary,Firefox']