diff --git a/src/Cite.php b/src/Cite.php
index bb9377807..ae984447c 100644
--- a/src/Cite.php
+++ b/src/Cite.php
@@ -305,7 +305,7 @@ class Cite {
 	private function formatReferences(
 		Parser $parser,
 		string $group,
-		string $responsive = null
+		?string $responsive = null
 	): string {
 		$responsiveReferences = $this->config->get( 'CiteResponsiveReferences' );
 
diff --git a/tests/phpunit/integration/CiteTest.php b/tests/phpunit/integration/CiteTest.php
index 7195cf5a6..d3b67cbee 100644
--- a/tests/phpunit/integration/CiteTest.php
+++ b/tests/phpunit/integration/CiteTest.php
@@ -28,7 +28,7 @@ class CiteTest extends \MediaWikiIntegrationTestCase {
 	public function testParseArguments(
 		array $attributes,
 		array $expectedValue,
-		string $expectedError = null
+		?string $expectedError = null
 	) {
 		/** @var Cite $cite */
 		$cite = TestingAccessWrapper::newFromObject( $this->newCite() );
diff --git a/tests/phpunit/unit/ErrorReporterTest.php b/tests/phpunit/unit/ErrorReporterTest.php
index 22b027faf..5ec2e5743 100644
--- a/tests/phpunit/unit/ErrorReporterTest.php
+++ b/tests/phpunit/unit/ErrorReporterTest.php
@@ -100,7 +100,7 @@ class ErrorReporterTest extends \MediaWikiUnitTestCase {
 		return new ErrorReporter( $mockMessageLocalizer );
 	}
 
-	private function createParser( Language $language, string $expectedCategory = null ): Parser {
+	private function createParser( Language $language, ?string $expectedCategory = null ): Parser {
 		$parserOptions = $this->createMock( ParserOptions::class );
 		$parserOptions->method( 'getUserLangObj' )->willReturn( $language );