diff --git a/includes/ULSJsonMessageLoader.php b/includes/ULSJsonMessageLoader.php
index 7b7334af..876bbe15 100644
--- a/includes/ULSJsonMessageLoader.php
+++ b/includes/ULSJsonMessageLoader.php
@@ -26,7 +26,7 @@ class ULSJsonMessageLoader {
 	 * @param string $language Language code.
 	 * @return string[]
 	 */
-	public static function getFilenames( $language ) {
+	public static function getFilenames( string $language ) {
 		$filenames = [];
 
 		$languages = Language::getFallbacksFor( $language );
@@ -54,7 +54,7 @@ class ULSJsonMessageLoader {
 	 * @param string $language Language code.
 	 * @return array
 	 */
-	public static function getMessages( $language ) {
+	public static function getMessages( string $language ) {
 		$contents = [];
 
 		foreach ( self::getFilenames( $language ) as $filename ) {
diff --git a/tests/phpunit/ULSJsonMessageLoaderTest.php b/tests/phpunit/ULSJsonMessageLoaderTest.php
index 16d093c3..9d5d14c3 100644
--- a/tests/phpunit/ULSJsonMessageLoaderTest.php
+++ b/tests/phpunit/ULSJsonMessageLoaderTest.php
@@ -15,14 +15,14 @@ class ULSJsonMessageLoaderTest extends \PHPUnit\Framework\TestCase {
 	public function testGetFilenamesWithBadInput() {
 		$instance = new ULSJsonMessageLoader();
 
-		$this->expectException( \Exception::class );
+		$this->expectException( \TypeError::class );
 		$instance->getFilenames( null );
 	}
 
 	public function testGetMessagesWithBadInput() {
 		$instance = new ULSJsonMessageLoader();
 
-		$this->expectException( \Exception::class );
+		$this->expectException( \TypeError::class );
 		$instance->getMessages( null );
 	}