diff --git a/prefixer/fix-swiftmailer.php b/prefixer/fix-swiftmailer.php
index 05966de439..cf86c2bfc1 100755
--- a/prefixer/fix-swiftmailer.php
+++ b/prefixer/fix-swiftmailer.php
@@ -14,6 +14,8 @@ foreach ($files as $file) {
     $data = preg_replace("/'(Swift_[^']*?::)/", "'MailPoetVendor\\\\\\\\$1", $data);
     $data = preg_replace("/InstanceOf\('(Swift_[^']*?')/", "InstanceOf('MailPoetVendor\\\\\\\\$1", $data);
     $data = preg_replace("/registerAutoload\('(_swift[^']*?')/", "registerAutoload('MailPoetVendor\\\\\\\\$1", $data);
+    $data = preg_replace("/'(Swift_[^']*?Listener)/", "'MailPoetVendor\\\\\\\\$1", $data);
+    $data = str_replace("'Swift_CharacterReader_", "'MailPoetVendor\\\\Swift_CharacterReader_", $data);
     $data = str_replace('SWIFT_INIT_LOADED', 'MAILPOET_SWIFT_INIT_LOADED', $data);
 
     // require-once 'swift_init.php' in classes since prefixed version won't use Swift's autoloader
diff --git a/tests/acceptance/ReceiveStandardEmailCest.php b/tests/acceptance/ReceiveStandardEmailCest.php
index 23376e0069..a4970d39db 100644
--- a/tests/acceptance/ReceiveStandardEmailCest.php
+++ b/tests/acceptance/ReceiveStandardEmailCest.php
@@ -17,7 +17,10 @@ class ReceiveStandardEmailCest {
   function receiveStandardEmail(\AcceptanceTester $I) {
     $this->settings->withCronTriggerMethod('WordPress');
 
-    $newsletter_title = 'Receive Test' . \MailPoet\Util\Security::generateRandomString();
+    // try some special characters in the subject to ensure they are received correctly
+    $special_chars = '… © & ěščřžýáíéůėꀿąß∂‍‍‍';
+
+    $newsletter_title = 'Receive Test ' . $special_chars;
     $standard_template = '[data-automation-id=\'select_template_0\']';
     $title_element = '[data-automation-id=\'newsletter_title\']';
     $send_form_element = '[data-automation-id="newsletter_send_form"]';
diff --git a/tests/integration/Mailer/Methods/AmazonSESTest.php b/tests/integration/Mailer/Methods/AmazonSESTest.php
index a194fc78ea..ba71d7736d 100644
--- a/tests/integration/Mailer/Methods/AmazonSESTest.php
+++ b/tests/integration/Mailer/Methods/AmazonSESTest.php
@@ -45,7 +45,7 @@ class AmazonSESTest extends \MailPoetTest {
     );
     $this->subscriber = 'Recipient <mailpoet-phoenix-test@mailinator.com>';
     $this->newsletter = [
-      'subject' => 'testing AmazonSES',
+      'subject' => 'testing AmazonSES … © & ěščřžýáíéůėꀿąß∂ 😊👨‍👩‍👧‍👧', // try some special chars
       'body' => [
         'html' => 'HTML body',
         'text' => 'TEXT body',
diff --git a/tests/integration/Mailer/Methods/MailPoetAPITest.php b/tests/integration/Mailer/Methods/MailPoetAPITest.php
index f2d710776a..555aa51b13 100644
--- a/tests/integration/Mailer/Methods/MailPoetAPITest.php
+++ b/tests/integration/Mailer/Methods/MailPoetAPITest.php
@@ -40,7 +40,7 @@ class MailPoetAPITest extends \MailPoetTest {
     );
     $this->subscriber = 'Recipient <mailpoet-phoenix-test@mailinator.com>';
     $this->newsletter = [
-      'subject' => 'testing MailPoet',
+      'subject' => 'testing MailPoet … © & ěščřžýáíéůėꀿąß∂ 😊👨‍👩‍👧‍👧', // try some special chars
       'body' => [
         'html' => 'HTML body',
         'text' => 'TEXT body',
diff --git a/tests/integration/Mailer/Methods/PHPMailTest.php b/tests/integration/Mailer/Methods/PHPMailTest.php
index 171bd00d4d..751f81cc8c 100644
--- a/tests/integration/Mailer/Methods/PHPMailTest.php
+++ b/tests/integration/Mailer/Methods/PHPMailTest.php
@@ -30,7 +30,7 @@ class PHPMailTest extends \MailPoetTest {
     );
     $this->subscriber = 'Recipient <mailpoet-phoenix-test@mailinator.com>';
     $this->newsletter = [
-      'subject' => 'testing local method (PHP mail)',
+      'subject' => 'testing local method (PHP mail) … © & ěščřžýáíéůėꀿąß∂ 😊👨‍👩‍👧‍👧', // try some special chars
       'body' => [
         'html' => 'HTML body',
         'text' => 'TEXT body',
diff --git a/tests/integration/Mailer/Methods/SMTPTest.php b/tests/integration/Mailer/Methods/SMTPTest.php
index 90c766e085..d4f30aa1e7 100644
--- a/tests/integration/Mailer/Methods/SMTPTest.php
+++ b/tests/integration/Mailer/Methods/SMTPTest.php
@@ -52,7 +52,7 @@ class SMTPTest extends \MailPoetTest {
     );
     $this->subscriber = 'Recipient <mailpoet-phoenix-test@mailinator.com>';
     $this->newsletter = [
-      'subject' => 'testing SMTP',
+      'subject' => 'testing SMTP … © & ěščřžýáíéůėꀿąß∂ 😊👨‍👩‍👧‍👧', // try some special chars
       'body' => [
         'html' => 'HTML body',
         'text' => 'TEXT body',
diff --git a/tests/integration/Mailer/Methods/SendGridTest.php b/tests/integration/Mailer/Methods/SendGridTest.php
index 6a1595e19e..ee60fd6167 100644
--- a/tests/integration/Mailer/Methods/SendGridTest.php
+++ b/tests/integration/Mailer/Methods/SendGridTest.php
@@ -35,7 +35,7 @@ class SendGridTest extends \MailPoetTest {
     );
     $this->subscriber = 'Recipient <mailpoet-phoenix-test@mailinator.com>';
     $this->newsletter = [
-      'subject' => 'testing SendGrid',
+      'subject' => 'testing SendGrid … © & ěščřžýáíéůėꀿąß∂ 😊👨‍👩‍👧‍👧', // try some special chars
       'body' => [
         'html' => 'HTML body',
         'text' => 'TEXT body',