diff --git a/src/Symfony/Component/HttpClient/Tests/HttplugClientTest.php b/src/Symfony/Component/HttpClient/Tests/HttplugClientTest.php
index 4f3e92d3e1..05ff05073a 100644
--- a/src/Symfony/Component/HttpClient/Tests/HttplugClientTest.php
+++ b/src/Symfony/Component/HttpClient/Tests/HttplugClientTest.php
@@ -22,7 +22,7 @@ class HttplugClientTest extends TestCase
 {
     private static $server;
 
-    public static function setUpBeforeClass()
+    public static function setUpBeforeClass(): void
     {
         TestHttpServer::start();
     }
diff --git a/src/Symfony/Contracts/HttpClient/Test/HttpClientTestCase.php b/src/Symfony/Contracts/HttpClient/Test/HttpClientTestCase.php
index 24cbfc3e1d..b5364ecab5 100644
--- a/src/Symfony/Contracts/HttpClient/Test/HttpClientTestCase.php
+++ b/src/Symfony/Contracts/HttpClient/Test/HttpClientTestCase.php
@@ -26,7 +26,7 @@ abstract class HttpClientTestCase extends TestCase
 {
     private static $server;
 
-    public static function setUpBeforeClass()
+    public static function setUpBeforeClass(): void
     {
         TestHttpServer::start();
     }