diff --git a/src/Contact/ContactService.php b/src/Contact/ContactService.php
index 6b3c468..eb1b187 100644
--- a/src/Contact/ContactService.php
+++ b/src/Contact/ContactService.php
@@ -205,7 +205,7 @@ private function prepareParams(AddContactCommand $addContactCommand, ContactCust
             unset($params['name']);
         }
 
-        if (!empty($addContactCommand->getDayOfCycle())) {
+        if (null !== $addContactCommand->getDayOfCycle()) {
             $params['dayOfCycle'] = $addContactCommand->getDayOfCycle();
         }
 
diff --git a/tests/Generator.php b/tests/Generator.php
index 7402026..202343f 100644
--- a/tests/Generator.php
+++ b/tests/Generator.php
@@ -232,9 +232,10 @@ private static function createHistoricalOrderCollection()
 
     /**
      * @param string $name
+     * @param int $dayOfCycle
      * @return AddContactCommand
      */
-    public static function createAddContactCommand($name = 'Adam Kowalski')
+    public static function createAddContactCommand($name = 'Adam Kowalski', $dayOfCycle = 3)
     {
         $customFieldCollection = new ContactCustomFieldsCollection();
         $customFieldCollection->add(new ContactCustomField('id_1',  'value_1'));
@@ -244,7 +245,7 @@ public static function createAddContactCommand($name = 'Adam Kowalski')
             'adam.kowalski@getresponse.com',
             $name,
             'contactListId',
-            3,
+            $dayOfCycle,
             $customFieldCollection,
             'origin'
         );
diff --git a/tests/Unit/Domain/Contact/ContactServiceTest.php b/tests/Unit/Domain/Contact/ContactServiceTest.php
index 1b36d5d..5280b6d 100644
--- a/tests/Unit/Domain/Contact/ContactServiceTest.php
+++ b/tests/Unit/Domain/Contact/ContactServiceTest.php
@@ -8,9 +8,9 @@
 use GrShareCode\Contact\ContactNotFoundException;
 use GrShareCode\Contact\ContactService;
 use GrShareCode\GetresponseApiClient;
+use GrShareCode\GetresponseApiException;
 use GrShareCode\Tests\Generator;
 use GrShareCode\Tests\Unit\BaseTestCase;
-use PHPUnit\Framework\TestCase;
 
 /**
  * Class ContactServiceTest
@@ -75,7 +75,7 @@ public function shouldThrowExceptionWhenClientNotExists()
      * @dataProvider validAddContactProvider
      * @param $addContactCommand
      * @param $params
-     * @throws \GrShareCode\GetresponseApiException
+     * @throws GetresponseApiException
      */
     public function shouldCreateContact($addContactCommand, $params)
     {
@@ -289,6 +289,83 @@ public function shouldCreateContactWithOriginIfCustomFieldNotExists()
         $contactService->createContact($addContactCommand);
     }
 
+    /**
+     * @test
+     */
+    public function shouldCreateContactWithDayOfCycleZero()
+    {
+        $customerName = 'Adam Kowalski';
+        $dayOfCycle = 0;
+
+        $params = [
+            'name' => $customerName,
+            'email' => 'adam.kowalski@getresponse.com',
+            'campaign' => [
+                'campaignId' => 'contactListId'
+            ],
+            'dayOfCycle' => $dayOfCycle,
+            'customFieldValues' => [
+                ['customFieldId' => 'id_1', 'value' => ['value_1']],
+                ['customFieldId' => 'id_2', 'value' => ['value_2']],
+                ['customFieldId' => 'cx4R', 'value' => ['origin']]
+            ]
+        ];
+
+        $this->getResponseApiClientMock
+            ->expects($this->once())
+            ->method('createContact')
+            ->with($params);
+
+        $this->getResponseApiClientMock
+            ->expects($this->once())
+            ->method('getCustomFieldByName')
+            ->with('origin')
+            ->willReturn(['customFieldId' => 'cx4R']);
+
+        $addContactCommand = Generator::createAddContactCommand($customerName, $dayOfCycle);
+
+        $contactService = new ContactService($this->getResponseApiClientMock);
+        $contactService->createContact($addContactCommand);
+    }
+
+    /**
+     * @test
+     */
+    public function shouldCreateContactWithNoDayOfCycle()
+    {
+        $customerName = 'Adam Kowalski';
+        $dayOfCycle = null;
+
+        $params = [
+            'name' => $customerName,
+            'email' => 'adam.kowalski@getresponse.com',
+            'campaign' => [
+                'campaignId' => 'contactListId'
+            ],
+            'customFieldValues' => [
+                ['customFieldId' => 'id_1', 'value' => ['value_1']],
+                ['customFieldId' => 'id_2', 'value' => ['value_2']],
+                ['customFieldId' => 'cx4R', 'value' => ['origin']]
+            ]
+        ];
+
+        $this->getResponseApiClientMock
+            ->expects($this->once())
+            ->method('createContact')
+            ->with($params);
+
+        $this->getResponseApiClientMock
+            ->expects($this->once())
+            ->method('getCustomFieldByName')
+            ->with('origin')
+            ->willReturn(['customFieldId' => 'cx4R']);
+
+        $addContactCommand = Generator::createAddContactCommand($customerName, $dayOfCycle);
+
+        $contactService = new ContactService($this->getResponseApiClientMock);
+        $contactService->createContact($addContactCommand);
+    }
+
     /**
      * @test
      */
@@ -351,6 +428,7 @@ public function shouldUnsubscribeContact()
      * @param string $email
      * @param string $origin
      * @param string $invalidOrigin
+     * @throws GetresponseApiException
      */
     public function shouldNotUnsubscribeContact($email, $origin, $invalidOrigin)
     {