diff --git a/lib/alpha_vantage.coffee b/lib/alpha_vantage.coffee
index 82f5271..ac20912 100644
--- a/lib/alpha_vantage.coffee
+++ b/lib/alpha_vantage.coffee
@@ -1,5 +1,6 @@
 QueryString = require './query_string'
 AlphaVantageTimeSeriesDaily = require './alpha_vantage/time_series_daily'
+AlphaVantageErrorMessage    = require './alpha_vantage/error_message'
 AlphaVantageSlackMessage    = require './alpha_vantage/slack_message'
 
 class AlphaVantage
@@ -22,7 +23,7 @@ class AlphaVantage
       .get() (error, response, body) ->
         result = JSON.parse(body)
         if result.hasOwnProperty('Error Message')
-          callback(attachments: [{ color: '#ff0000', title: 'Error Message', text: result['Error Message'] }])
+          callback(new AlphaVantageErrorMessage(result))
         else
           outline = new AlphaVantageTimeSeriesDaily(result).outline()
           callback(new AlphaVantageSlackMessage(outline))
diff --git a/lib/alpha_vantage/error_message.coffee b/lib/alpha_vantage/error_message.coffee
new file mode 100644
index 0000000..f4458ae
--- /dev/null
+++ b/lib/alpha_vantage/error_message.coffee
@@ -0,0 +1,13 @@
+class AlphaVantageErrorMessage
+  _response = undefined
+
+  constructor: (response) ->
+    _response = response
+
+  format: ->
+    return attachments: [{ color: '#FF0000', title: 'Error Message', text: _response['Error Message'] }]
+
+  toString: ->
+    return JSON.stringify(@format())
+
+module.exports = AlphaVantageErrorMessage
diff --git a/test/fixture/error_message.json b/test/fixture/error_message.json
new file mode 100644
index 0000000..ca935a7
--- /dev/null
+++ b/test/fixture/error_message.json
@@ -0,0 +1,3 @@
+{
+    "Error Message": "Invalid API call."
+}
diff --git a/test/lib/alpha_vantage.coffee b/test/lib/alpha_vantage.coffee
index 213d746..a5d7f63 100644
--- a/test/lib/alpha_vantage.coffee
+++ b/test/lib/alpha_vantage.coffee
@@ -5,6 +5,7 @@ sinon  = require('sinon')
 
 Robot = require('hubot/src/robot')
 AlphaVantageSlackMessage = require '../../lib/alpha_vantage/slack_message'
+AlphaVantageErrorMessage = require '../../lib/alpha_vantage/error_message'
 AlphaVantage = require(source)
 describe 'AlphaVantage', ->
 
@@ -37,9 +38,18 @@ describe 'AlphaVantage', ->
     afterEach ->
       robot.http.restore()
 
-    it 'returns an instance with default values', () ->
-      http_stub((f) -> f('error', 'response', helper.fixture.time_series_daily))
+    describe 'when response is successful', ->
+      it 'calls callback with a message object ', () ->
+        http_stub((f) -> f('error', 'response', helper.fixture.time_series_daily))
+
+        new AlphaVantage(function: 'FUNCTION', symbol: 'SYMBOL').execute(robot, (message) ->
+          expect(message).to.be.an.instanceof(AlphaVantageSlackMessage)
+        )
 
-      av = new AlphaVantage(function: 'FUNCTION', symbol: 'SYMBOL').execute(robot, (message) ->
-        expect(message).to.be.an.instanceof(AlphaVantageSlackMessage)
-      )
+    describe 'when response is failure', ->
+      it 'calls callback with a message object ', () ->
+        http_stub((f) -> f('error', 'response', helper.fixture.error_message))
+
+        new AlphaVantage(function: 'FUNCTION', symbol: 'SYMBOL').execute(robot, (message) ->
+          expect(message).to.be.an.instanceof(AlphaVantageErrorMessage)
+        )
diff --git a/test/lib/alpha_vantage/error_message.coffee b/test/lib/alpha_vantage/error_message.coffee
new file mode 100644
index 0000000..06393af
--- /dev/null
+++ b/test/lib/alpha_vantage/error_message.coffee
@@ -0,0 +1,17 @@
+source = '../../../lib/alpha_vantage/error_message'
+helper = require('../../test_helper')
+expect = require('chai').expect
+
+AlphaVantageErrorMessage = require(source)
+describe 'AlphaVantageErrorMessage', ->
+  subject = undefined
+
+  beforeEach ->
+    object  = { 'Error Message': 'Invalid API call.' }
+    subject = new AlphaVantageErrorMessage(object)
+
+  describe '#format', ->
+    it 'returns a object for slack message', () ->
+      expect(subject.format().attachments).to.have.ordered.deep.members([
+        { color: '#FF0000', title: 'Error Message', text: 'Invalid API call.' }
+      ])
diff --git a/test/lib/alpha_vantage/slack_message.coffee b/test/lib/alpha_vantage/slack_message.coffee
index abe1e69..a3b8713 100644
--- a/test/lib/alpha_vantage/slack_message.coffee
+++ b/test/lib/alpha_vantage/slack_message.coffee
@@ -20,7 +20,7 @@ describe 'AlphaVantageSlackMessage', ->
     subject = new AlphaVantageSlackMessage(object)
 
   describe '#format', ->
-    it 'returns a string', () ->
+    it 'returns a object for slack message', () ->
       expect(subject.format()).to.include(text: 'MSFT *149.85* at December 4, 2019', mrkdwn: true)
       expect(subject.format().attachments).to.have.ordered.deep.members([
         { color: '#35A64F', text: '+0.54 (+0.36%) at December 3, 2019' }
diff --git a/test/test_helper.coffee b/test/test_helper.coffee
index 198ebe5..966d63f 100644
--- a/test/test_helper.coffee
+++ b/test/test_helper.coffee
@@ -4,4 +4,5 @@ moment = require('moment-timezone')
 
 exports.moment  = moment
 exports.fixture =
+  error_message:     fs.readFileSync(path.join(__dirname, './fixture/error_message.json'))
   time_series_daily: fs.readFileSync(path.join(__dirname, './fixture/time_series_daily.json'))