diff --git a/src/Data/AlphaNum.php b/src/Data/AlphaNum.php
index ec86e471d..cb9c89371 100644
--- a/src/Data/AlphaNum.php
+++ b/src/Data/AlphaNum.php
@@ -44,7 +44,7 @@ class AlphaNum extends QRDataAbstract{
 	 * @throws \chillerlan\QRCode\Data\QRCodeDataException
 	 */
 	protected function getCharCode(string $chr):int{
-		$i = array_search($chr, $this::ALPHANUM_CHAR_MAP);
+		$i = array_search($chr, $this::CHAR_MAP_ALPHANUM);
 
 		if($i !== false){
 			return $i;
diff --git a/src/Data/Number.php b/src/Data/Number.php
index d0b33619a..b97a6a564 100644
--- a/src/Data/Number.php
+++ b/src/Data/Number.php
@@ -59,7 +59,7 @@ class Number extends QRDataAbstract{
 		for($i = 0; $i < $len; $i++){
 			$c = ord($string[$i]);
 
-			if(!in_array($string[$i], $this::NUMBER_CHAR_MAP, true)){
+			if(!in_array($string[$i], $this::CHAR_MAP_NUMBER, true)){
 				throw new QRCodeDataException(sprintf('illegal char: "%s" [%d]', $string[$i], $c));
 			}
 
diff --git a/src/Data/QRDataInterface.php b/src/Data/QRDataInterface.php
index 936374a4f..9d0f40d13 100644
--- a/src/Data/QRDataInterface.php
+++ b/src/Data/QRDataInterface.php
@@ -17,9 +17,12 @@ namespace chillerlan\QRCode\Data;
  */
 interface QRDataInterface{
 
-	const NUMBER_CHAR_MAP = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9'];
+	const CHAR_MAP_NUMBER = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9'];
 
-	const ALPHANUM_CHAR_MAP = [
+	/**
+	 * ISO/IEC 18004:2000 Table 5
+	 */
+	const CHAR_MAP_ALPHANUM = [
 		'0', '1', '2', '3', '4', '5', '6', '7',
 		'8', '9', 'A', 'B', 'C', 'D', 'E', 'F',
 		'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N',
diff --git a/src/QRCode.php b/src/QRCode.php
index ae0efef59..c29346d40 100755
--- a/src/QRCode.php
+++ b/src/QRCode.php
@@ -229,14 +229,14 @@ class QRCode{
 	 * checks if a string qualifies as numeric
 	 */
 	public function isNumber(string $string):bool{
-		return $this->checkString($string, QRDataInterface::NUMBER_CHAR_MAP);
+		return $this->checkString($string, QRDataInterface::CHAR_MAP_NUMBER);
 	}
 
 	/**
 	 * checks if a string qualifies as alphanumeric
 	 */
 	public function isAlphaNum(string $string):bool{
-		return $this->checkString($string, QRDataInterface::ALPHANUM_CHAR_MAP);
+		return $this->checkString($string, QRDataInterface::CHAR_MAP_ALPHANUM);
 	}
 
 	/**