diff --git a/src/MessageBird/Client.php b/src/MessageBird/Client.php
index 91aff4cc..5f97416d 100644
--- a/src/MessageBird/Client.php
+++ b/src/MessageBird/Client.php
@@ -12,7 +12,7 @@ class Client
     const ENDPOINT = 'https://rest.messagebird.com';
     const CHATAPI_ENDPOINT = 'https://chat.messagebird.com/1';
 
-    const CLIENT_VERSION = '1.6.5';
+    const CLIENT_VERSION = '1.6.6';
 
     /**
      * @var string
diff --git a/src/MessageBird/Objects/VoiceMessage.php b/src/MessageBird/Objects/VoiceMessage.php
index 7381ebbb..bb72c7ff 100644
--- a/src/MessageBird/Objects/VoiceMessage.php
+++ b/src/MessageBird/Objects/VoiceMessage.php
@@ -81,6 +81,14 @@ class VoiceMessage extends Base
      */
     public $ifMachine = 'continue';
 
+    /**
+     * The time (in milliseconds) to analyze if a machine has picked up the phone. Used in combination with the delay
+     * and hangup values of the ifMachine attribute. Minimum: 400, maximum: 10000.
+     *
+     * @var int
+     */
+    public $machineTimeout = 7000;
+
     /**
      * The scheduled date and time of the message in RFC3339 format (Y-m-d\TH:i:sP)
      *
diff --git a/tests/integration/voicemessages/VoiceMessagesTest.php b/tests/integration/voicemessages/VoiceMessagesTest.php
index e4f3bb31..c9d858f7 100644
--- a/tests/integration/voicemessages/VoiceMessagesTest.php
+++ b/tests/integration/voicemessages/VoiceMessagesTest.php
@@ -18,7 +18,7 @@ public function testVoiceMessageCreate()
         $Message->body       = 'This is a test message.';
         $Message->language   = "nl";
         $Message->voice      = "male";
-        $this->mockClient->expects($this->once())->method('performHttpRequest')->with("POST", 'voicemessages', null, '{"originator":"MessageBird","body":"This is a test message.","reference":null,"language":"nl","voice":"male","repeat":1,"ifMachine":"continue","scheduledDatetime":null,"recipients":[31612345678],"reportUrl":null}');
+        $this->mockClient->expects($this->once())->method('performHttpRequest')->with("POST", 'voicemessages', null, '{"originator":"MessageBird","body":"This is a test message.","reference":null,"language":"nl","voice":"male","repeat":1,"ifMachine":"continue","machineTimeout":7000,"scheduledDatetime":null,"recipients":[31612345678],"reportUrl":null}');
         $this->client->voicemessages->create($Message);
     }