diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 9ea164fa..da699d6e 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -46,7 +46,7 @@ jobs:
           php-version: ${{ matrix.php }}
           coverage: xdebug
           ini-values: sendmail_path=/usr/sbin/sendmail -t -i, zend.multibyte=1, zend.script_encoding=UTF-8, default_charset=UTF-8
-          extensions: xdebug, imap, mbstring, ctype, filter, hash
+          extensions: xdebug, imap, mbstring, intl, ctype, filter, hash
 
       - name: Install PHP packages
         run: composer install --no-interaction
diff --git a/test/PHPMailerTest.php b/test/PHPMailerTest.php
index 1164f6a4..3d4f8a66 100644
--- a/test/PHPMailerTest.php
+++ b/test/PHPMailerTest.php
@@ -901,25 +901,26 @@ final class PHPMailerTest extends TestCase
         $this->Mail->isMail();
         //Expected results
 
-        $bencoderes = '=?UTF-8?B?w6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6k=?=' .
+        $bencoderes = '=?utf-8?B?w6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6k=?=' .
             PHPMailer::getLE() .
-            ' =?UTF-8?B?w6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6k=?=' .
+            ' =?utf-8?B?w6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6k=?=' .
             PHPMailer::getLE() .
-            ' =?UTF-8?B?w6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6k=?=' .
+            ' =?utf-8?B?w6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6k=?=' .
             PHPMailer::getLE() .
-            ' =?UTF-8?B?w6nDqcOpw6nDqcOpw6nDqcOpw6nDqQ==?=';
-        $qencoderes = '=?UTF-8?Q?eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee?=' .
+            ' =?utf-8?B?w6nDqcOpw6nDqcOpw6nDqcOpw6nDqQ==?=';
+        $qencoderes = '=?utf-8?Q?eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee?=' .
             PHPMailer::getLE() .
-            ' =?UTF-8?Q?eeeeeeeeeeeeeeeeeeeeeeeeee=C3=A9?=';
-        $bencodenofoldres = '=?UTF-8?B?w6nDqcOpw6nDqcOpw6nDqcOpw6k=?=';
-        $qencodenofoldres = '=?UTF-8?Q?eeeeeeeee=C3=A9?=';
+            ' =?utf-8?Q?eeeeeeeeeeeeeeeeeeeeeeeeee=C3=A9?=';
+        $bencodenofoldres = '=?utf-8?B?w6nDqcOpw6nDqcOpw6nDqcOpw6k=?=';
+        $qencodenofoldres = '=?utf-8?Q?eeeeeeeee=C3=A9?=';
         $longheaderres = '=?us-ascii?Q?eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee?=' .
             PHPMailer::getLE() . ' =?us-ascii?Q?eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee?=';
-        $longutf8res = '=?UTF-8?B?w6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6k=?=' .
-             PHPMailer::getLE() . ' =?UTF-8?B?w6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6k=?=' .
-             PHPMailer::getLE() . ' =?UTF-8?B?w6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6k=?=' .
-             PHPMailer::getLE() . ' =?UTF-8?B?w6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqQ==?=';
+        $longutf8res = '=?utf-8?B?w6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6k=?=' .
+             PHPMailer::getLE() . ' =?utf-8?B?w6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6k=?=' .
+             PHPMailer::getLE() . ' =?utf-8?B?w6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6k=?=' .
+             PHPMailer::getLE() . ' =?utf-8?B?w6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqcOpw6nDqQ==?=';
         $noencoderes = 'eeeeeeeeee';
+        $this->Mail->CharSet = PHPMailer::CHARSET_UTF8;
         self::assertEquals(
             $bencoderes,
             $this->Mail->encodeHeader($bencode),
@@ -3116,8 +3117,14 @@ EOT;
     {
         if (file_exists($this->INCLUDE_DIR . '/test/fakefunctions.php')) {
             include $this->INCLUDE_DIR . '/test/fakefunctions.php';
+            //This source file is in UTF-8, so characters here are in native charset
+            $this->Mail->CharSet = PHPMailer::CHARSET_UTF8;
             $result = $this->Mail->punyencodeAddress('test@françois.ch');
-            $this->assertEquals('test@xn--franois-bja35c.ch', $result);
+            $this->assertEquals('test@xn--franois-xxa.ch', $result);
+            //To force working another charset, decode an ASCII string to avoid literal string charset issues
+            $this->Mail->CharSet = PHPMailer::CHARSET_ISO88591;
+            $result = $this->Mail->punyencodeAddress(html_entity_decode('test@françois.ch', ENT_COMPAT, 'ISO-8859-1'));
+            $this->assertEquals('test@xn--franois-xxa.ch', $result);
         }
     }