diff --git a/tests/acceptance/Swift/Mime/AttachmentAcceptanceTest.php b/tests/acceptance/Swift/Mime/AttachmentAcceptanceTest.php
index 920faed9b..11666b5be 100644
--- a/tests/acceptance/Swift/Mime/AttachmentAcceptanceTest.php
+++ b/tests/acceptance/Swift/Mime/AttachmentAcceptanceTest.php
@@ -8,6 +8,7 @@ class Swift_Mime_AttachmentAcceptanceTest extends \PHPUnit\Framework\TestCase
     private $cache;
     private $headers;
     private $emailValidator;
+    private $idGenerator;
 
     protected function setUp()
     {
diff --git a/tests/acceptance/Swift/Mime/EmbeddedFileAcceptanceTest.php b/tests/acceptance/Swift/Mime/EmbeddedFileAcceptanceTest.php
index 5603a67d7..3e614854d 100644
--- a/tests/acceptance/Swift/Mime/EmbeddedFileAcceptanceTest.php
+++ b/tests/acceptance/Swift/Mime/EmbeddedFileAcceptanceTest.php
@@ -8,6 +8,7 @@ class Swift_Mime_EmbeddedFileAcceptanceTest extends \PHPUnit\Framework\TestCase
     private $cache;
     private $headers;
     private $emailValidator;
+    private $idGenerator;
 
     protected function setUp()
     {
diff --git a/tests/acceptance/Swift/Mime/MimePartAcceptanceTest.php b/tests/acceptance/Swift/Mime/MimePartAcceptanceTest.php
index 5a12daad7..93780ee08 100644
--- a/tests/acceptance/Swift/Mime/MimePartAcceptanceTest.php
+++ b/tests/acceptance/Swift/Mime/MimePartAcceptanceTest.php
@@ -8,6 +8,7 @@ class Swift_Mime_MimePartAcceptanceTest extends \PHPUnit\Framework\TestCase
     private $cache;
     private $headers;
     private $emailValidator;
+    private $idGenerator;
 
     protected function setUp()
     {