diff --git a/composer.json b/composer.json
index e7f7d6c..299266b 100644
--- a/composer.json
+++ b/composer.json
@@ -30,7 +30,7 @@
 	"require-dev": {
 		"phpunit/phpunit": "~8.0",
 		"ockcyp/covers-validator": "^1.3.3",
-		"mediawiki/mediawiki-codesniffer": "^34"
+		"mediawiki/mediawiki-codesniffer": "45.0.0"
 	},
 	"extra": {
 		"branch-alias": {
@@ -67,5 +67,10 @@
 			"@cs",
 			"@test"
 		]
+	},
+	"config": {
+		"allow-plugins": {
+			"dealerdirect/phpcodesniffer-composer-installer": true
+		}
 	}
 }
diff --git a/phpcs.xml b/phpcs.xml
index 8649f80..52b4a07 100644
--- a/phpcs.xml
+++ b/phpcs.xml
@@ -7,4 +7,5 @@
 		<exclude name="Generic.Files.LineLength.TooLong" />
 		<exclude name="Generic.Files.LineLength.MaxExceeded" />
 	</rule>
+	<rule ref="./vendor/mediawiki/mediawiki-codesniffer/MediaWiki"/>
 </ruleset>
diff --git a/src/DataValues/MonolingualTextValue.php b/src/DataValues/MonolingualTextValue.php
index 03eb876..e331064 100644
--- a/src/DataValues/MonolingualTextValue.php
+++ b/src/DataValues/MonolingualTextValue.php
@@ -65,7 +65,7 @@ public function unserialize( $value ) {
 	}
 
 	public function __unserialize( array $data ): void {
-		list( $languageCode, $text ) = $data;
+		[ $languageCode, $text ] = $data;
 		$this->__construct( $languageCode, $text );
 	}
 
diff --git a/src/ValueFormatters/Exceptions/MismatchingDataValueTypeException.php b/src/ValueFormatters/Exceptions/MismatchingDataValueTypeException.php
index 549c79d..1c25dec 100644
--- a/src/ValueFormatters/Exceptions/MismatchingDataValueTypeException.php
+++ b/src/ValueFormatters/Exceptions/MismatchingDataValueTypeException.php
@@ -36,7 +36,7 @@ public function __construct(
 		$expectedValueType,
 		$dataValueType,
 		$message = '',
-		Exception $previous = null
+		?Exception $previous = null
 	) {
 		$this->expectedValueType = $expectedValueType;
 		$this->dataValueType = $dataValueType;
diff --git a/src/ValueParsers/BoolParser.php b/src/ValueParsers/BoolParser.php
index 5583073..99faf7f 100644
--- a/src/ValueParsers/BoolParser.php
+++ b/src/ValueParsers/BoolParser.php
@@ -18,6 +18,10 @@ class BoolParser extends StringValueParser {
 
 	private const FORMAT_NAME = 'bool';
 
+	/**
+	 * @var Mapping from possible string values to their
+	 *      boolean equivalents
+	 */
 	private static $values = [
 		'yes' => true,
 		'on' => true,
diff --git a/src/ValueParsers/StringParser.php b/src/ValueParsers/StringParser.php
index 3efb4bf..4827694 100644
--- a/src/ValueParsers/StringParser.php
+++ b/src/ValueParsers/StringParser.php
@@ -26,7 +26,7 @@ class StringParser implements ValueParser {
 	/**
 	 * @param StringNormalizer|null $normalizer
 	 */
-	public function __construct( StringNormalizer $normalizer = null ) {
+	public function __construct( ?StringNormalizer $normalizer = null ) {
 		$this->normalizer = $normalizer ?: new NullStringNormalizer();
 	}
 
diff --git a/src/ValueParsers/StringValueParser.php b/src/ValueParsers/StringValueParser.php
index c80e3c3..ac638c0 100644
--- a/src/ValueParsers/StringValueParser.php
+++ b/src/ValueParsers/StringValueParser.php
@@ -28,7 +28,7 @@ abstract class StringValueParser implements ValueParser {
 	/**
 	 * @param ParserOptions|null $options
 	 */
-	public function __construct( ParserOptions $options = null ) {
+	public function __construct( ?ParserOptions $options = null ) {
 		$this->options = $options ?: new ParserOptions();
 
 		$this->defaultOption( ValueParser::OPT_LANG, 'en' );
diff --git a/tests/ValueParsers/DispatchingValueParserTest.php b/tests/ValueParsers/DispatchingValueParserTest.php
index 0a547a7..7d42056 100644
--- a/tests/ValueParsers/DispatchingValueParserTest.php
+++ b/tests/ValueParsers/DispatchingValueParserTest.php
@@ -22,17 +22,17 @@
  */
 class DispatchingValueParserTest extends TestCase {
 
-	private function getParser( $invocation ) : ValueParser {
+	private function getParser( $invocation ): ValueParser {
 		$mock = $this->createMock( ValueParser::class );
 
 		$mock->expects( $invocation )
 			->method( 'parse' )
-			->will( $this->returnCallback( function( $value ) {
+			->willReturnCallback( static function ( $value ) {
 				if ( $value === 'invalid' ) {
 					throw new ParseException( 'failed' );
 				}
 				return $value;
-			} ) );
+			} );
 
 		return $mock;
 	}
diff --git a/tests/ValueParsers/NullParserTest.php b/tests/ValueParsers/NullParserTest.php
index 68a2af5..1f1573e 100644
--- a/tests/ValueParsers/NullParserTest.php
+++ b/tests/ValueParsers/NullParserTest.php
@@ -55,7 +55,7 @@ public function invalidInputProvider() {
 	 *
 	 * @dataProvider invalidInputProvider
 	 */
-	public function testParseWithInvalidInputs( $value, ValueParser $parser = null ) {
+	public function testParseWithInvalidInputs( $value, ?ValueParser $parser = null ) {
 		$this->markTestSkipped( 'NullParser has no invalid inputs' );
 	}
 
diff --git a/tests/ValueParsers/StringParserTest.php b/tests/ValueParsers/StringParserTest.php
index 410f2d4..c707846 100644
--- a/tests/ValueParsers/StringParserTest.php
+++ b/tests/ValueParsers/StringParserTest.php
@@ -26,9 +26,9 @@ public function provideParse() {
 		$normalizer = $this->createMock( StringNormalizer::class );
 		$normalizer->expects( $this->once() )
 			->method( 'normalize' )
-			->will( $this->returnCallback( function( $value ) {
+			->willReturnCallback( static function ( $value ) {
 				return strtolower( trim( $value ) );
-			} ) );
+			} );
 
 		return [
 			'simple' => [ 'hello world', null, new StringValue( 'hello world' ) ],
diff --git a/tests/ValueParsers/ValueParserTestBase.php b/tests/ValueParsers/ValueParserTestBase.php
index 6e57c32..cf5fdd9 100644
--- a/tests/ValueParsers/ValueParserTestBase.php
+++ b/tests/ValueParsers/ValueParserTestBase.php
@@ -44,7 +44,7 @@ abstract protected function getInstance();
 	 * @param mixed $expected
 	 * @param ValueParser|null $parser
 	 */
-	public function testParseWithValidInputs( $value, $expected, ValueParser $parser = null ) {
+	public function testParseWithValidInputs( $value, $expected, ?ValueParser $parser = null ) {
 		if ( $parser === null ) {
 			$parser = $this->getInstance();
 		}
@@ -77,7 +77,7 @@ private function assertSmartEquals( $expected, $actual ) {
 	 * @param mixed $value
 	 * @param ValueParser|null $parser
 	 */
-	public function testParseWithInvalidInputs( $value, ValueParser $parser = null ) {
+	public function testParseWithInvalidInputs( $value, ?ValueParser $parser = null ) {
 		if ( $parser === null ) {
 			$parser = $this->getInstance();
 		}