diff --git a/src/Data/AlphaNum.php b/src/Data/AlphaNum.php
index cb9c89371..9cfde177b 100644
--- a/src/Data/AlphaNum.php
+++ b/src/Data/AlphaNum.php
@@ -19,7 +19,7 @@ use function array_search, ord, sprintf;
 /**
  * Alphanumeric mode: 0 to 9, A to Z, space, $ % * + - . / :
  */
-class AlphaNum extends QRDataAbstract{
+final class AlphaNum extends QRDataAbstract{
 
 	protected int $datamode = QRCode::DATA_ALPHANUM;
 
diff --git a/src/Data/Byte.php b/src/Data/Byte.php
index de2f5b584..b4fe4309c 100644
--- a/src/Data/Byte.php
+++ b/src/Data/Byte.php
@@ -19,7 +19,7 @@ use function ord;
 /**
  * Byte mode, ISO-8859-1 or UTF-8
  */
-class Byte extends QRDataAbstract{
+final class Byte extends QRDataAbstract{
 
 	protected int $datamode = QRCode::DATA_BYTE;
 
diff --git a/src/Data/Kanji.php b/src/Data/Kanji.php
index 9a1b3787a..12f7a6b7c 100644
--- a/src/Data/Kanji.php
+++ b/src/Data/Kanji.php
@@ -19,7 +19,7 @@ use function mb_strlen, ord, sprintf, strlen;
 /**
  * Kanji mode: double-byte characters from the Shift JIS character set
  */
-class Kanji extends QRDataAbstract{
+final class Kanji extends QRDataAbstract{
 
 	protected int $datamode = QRCode::DATA_KANJI;
 
diff --git a/src/Data/MaskPatternTester.php b/src/Data/MaskPatternTester.php
index c93485e39..1fa44c9f8 100644
--- a/src/Data/MaskPatternTester.php
+++ b/src/Data/MaskPatternTester.php
@@ -19,7 +19,7 @@ use function abs, call_user_func;
  *
  * @link http://www.thonky.com/qr-code-tutorial/data-masking
  */
-class MaskPatternTester{
+final class MaskPatternTester{
 
 	protected QRMatrix $matrix;
 
diff --git a/src/Data/Number.php b/src/Data/Number.php
index b97a6a564..ab03a70cd 100644
--- a/src/Data/Number.php
+++ b/src/Data/Number.php
@@ -19,7 +19,7 @@ use function ord, sprintf, substr;
 /**
  * Numeric mode: decimal digits 0 through 9
  */
-class Number extends QRDataAbstract{
+final class Number extends QRDataAbstract{
 
 	protected int $datamode = QRCode::DATA_NUMBER;
 
diff --git a/src/Data/QRMatrix.php b/src/Data/QRMatrix.php
index 4222410c1..8fd056c8d 100755
--- a/src/Data/QRMatrix.php
+++ b/src/Data/QRMatrix.php
@@ -20,7 +20,7 @@ use function array_fill, array_key_exists, array_push, array_unshift, count, flo
 /**
  * @link http://www.thonky.com/qr-code-tutorial/format-version-information
  */
-class QRMatrix{
+final class QRMatrix{
 
 	public const M_NULL       = 0x00;
 	public const M_DARKMODULE = 0x02;
diff --git a/src/Helpers/BitBuffer.php b/src/Helpers/BitBuffer.php
index 84652929b..08fa32d45 100644
--- a/src/Helpers/BitBuffer.php
+++ b/src/Helpers/BitBuffer.php
@@ -14,7 +14,7 @@ namespace chillerlan\QRCode\Helpers;
 
 use function count, floor;
 
-class BitBuffer{
+final class BitBuffer{
 
 	/** @var int[] */
 	public array $buffer = [];
diff --git a/src/Helpers/Polynomial.php b/src/Helpers/Polynomial.php
index 4db2b2f7f..12c3f0078 100644
--- a/src/Helpers/Polynomial.php
+++ b/src/Helpers/Polynomial.php
@@ -19,7 +19,7 @@ use function array_fill, count, sprintf;
 /**
  * @link http://www.thonky.com/qr-code-tutorial/error-correction-coding
  */
-class Polynomial{
+final class Polynomial{
 
 	/**
 	 * @link http://www.thonky.com/qr-code-tutorial/log-antilog-table