diff --git a/.github/workflows/main.yaml b/.github/workflows/main.yaml
index 53d55a6..a26f0da 100644
--- a/.github/workflows/main.yaml
+++ b/.github/workflows/main.yaml
@@ -60,7 +60,7 @@ jobs:
 
     strategy:
       matrix:
-        php-version: [ '8.1', '8.2', '8.3', '8.4' ]
+        php-version: [ '8.1', '8.2', '8.3', '8.4', '8.5' ]
         operating-system: [ 'ubuntu-latest' ]
         composer-args: [ '' ]
         include:
diff --git a/src/CompanyRegistrationNumber.php b/src/CompanyRegistrationNumber.php
index b371fef..c7fdec1 100644
--- a/src/CompanyRegistrationNumber.php
+++ b/src/CompanyRegistrationNumber.php
@@ -98,7 +98,7 @@ private function isValidIE(
 
 		$remainder = $sum % 23;
 
-		return \chr(\ord('A') - 1 + $remainder) === $value[7];
+		return \mb_chr(\ord('A') - 1 + $remainder, 'UTF-8') === $value[7];
 	}
 
 	private function isValidCH(
diff --git a/src/Helpers/StringHelpers.php b/src/Helpers/StringHelpers.php
index a097c61..b3e6c36 100644
--- a/src/Helpers/StringHelpers.php
+++ b/src/Helpers/StringHelpers.php
@@ -65,7 +65,7 @@ final public static function removeWhitespace(
 		$replaceTable = [];
 
 		foreach (InvisibleSpaceCharacterCodes::getCodes() as $charCode) {
-			$replaceTable[\chr($charCode)] = '';
+			$replaceTable[\mb_chr($charCode, 'UTF-8')] = '';
 		}
 
 		return \strtr(
diff --git a/tools/cs/ruleset.xml b/tools/cs/ruleset.xml
index 26230f7..5d363e1 100644
--- a/tools/cs/ruleset.xml
+++ b/tools/cs/ruleset.xml
@@ -32,6 +32,7 @@
 		<exclude name="SlevomatCodingStandard.Arrays.AlphabeticallySortedByKeys.IncorrectKeyOrder"/>
 		<exclude name="SlevomatCodingStandard.Classes.RequireSelfReference.RequiredSelfReference"/>
 		<exclude name="SlevomatCodingStandard.Numbers.DisallowNumericLiteralSeparator.DisallowedNumericLiteralSeparator"/>
+		<exclude name="SlevomatCodingStandard.Classes.TraitUseOrder.IncorrectOrder"/>
 
 		<!-- TODO Enable after migration to PHP 8.1 -->
 		<exclude name="SlevomatCodingStandard.Functions.FunctionLength.FunctionLength"/>