diff --git a/Tests/MessageTest.php b/Tests/MessageTest.php
index 460da49..678be96 100644
--- a/Tests/MessageTest.php
+++ b/Tests/MessageTest.php
@@ -306,7 +306,7 @@ public function testEnsureValidity(array $headers, ?string $exceptionClass, ?str
         $m->ensureValidity();
     }
 
-    public function ensureValidityProvider()
+    public static function ensureValidityProvider(): array
     {
         return [
             'Valid address fields' => [