diff --git a/tests/BaseTestCase.php b/tests/BaseTestCase.php
index b441cab..89adbc0 100644
--- a/tests/BaseTestCase.php
+++ b/tests/BaseTestCase.php
@@ -11,7 +11,7 @@
 
 class BaseTestCase extends TestCase
 {
-    public function setUp()
+    public function setUp(): void
     {
         parent::setUp();
 
diff --git a/tests/MailViewerTest.php b/tests/MailViewerTest.php
index 79324d4..3c5cbd2 100644
--- a/tests/MailViewerTest.php
+++ b/tests/MailViewerTest.php
@@ -6,7 +6,7 @@ class MailViewerTest extends BaseTestCase
 {
     protected $packageUrl;
 
-    public function setUp()
+    public function setUp(): void
     {
         parent::setUp();