diff --git a/.travis.yml b/.travis.yml
index 88db786..3e74fb1 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -16,7 +16,6 @@ matrix:
     - php: 7.3
     - php: 7.4
     - php: hhvm-3.18
-      install: composer require phpunit/phpunit:^5 --dev --no-interaction # requires legacy phpunit
   allow_failures:
     - php: hhvm-3.18
 
diff --git a/composer.json b/composer.json
index 5f99c59..f3420b8 100644
--- a/composer.json
+++ b/composer.json
@@ -23,6 +23,6 @@
         "react/promise": "^3.0 || ^2.7.0 || ^1.2.1"
     },
     "require-dev": {
-        "phpunit/phpunit": "^7.0 || ^6.4 || ^5.7 || ^4.8.35"
+        "phpunit/phpunit": "^9.0 || ^5.7 || ^4.8.35"
     }
 }
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index bb79fba..1685bd1 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,11 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 
-<phpunit bootstrap="vendor/autoload.php"
-         colors="true"
-         convertErrorsToExceptions="true"
-         convertNoticesToExceptions="true"
-         convertWarningsToExceptions="true"
->
+<phpunit bootstrap="vendor/autoload.php" colors="true">
     <testsuites>
         <testsuite name="Promise Timer Test Suite">
             <directory>./tests/</directory>
diff --git a/tests/CallableStub.php b/tests/CallableStub.php
deleted file mode 100644
index a391aa5..0000000
--- a/tests/CallableStub.php
+++ /dev/null
@@ -1,10 +0,0 @@
-<?php
-
-namespace React\Tests\Promise\Timer;
-
-class CallableStub
-{
-    public function __invoke()
-    {
-    }
-}
diff --git a/tests/TestCase.php b/tests/TestCase.php
index 9d8d49a..bb7af5a 100644
--- a/tests/TestCase.php
+++ b/tests/TestCase.php
@@ -9,7 +9,10 @@ class TestCase extends BaseTestCase
 {
     protected $loop;
 
-    public function setUp()
+    /**
+     * @before
+     */
+    public function setUpLoop()
     {
         $this->loop = Factory::create();
     }
@@ -41,7 +44,13 @@ protected function expectCallableNever()
      */
     protected function createCallableMock()
     {
-        return $this->getMockBuilder('React\Tests\Promise\Timer\CallableStub')->getMock();
+        if (method_exists('PHPUnit\Framework\MockObject\MockBuilder', 'addMethods')) {
+            // PHPUnit 9+
+            return $this->getMockBuilder('stdClass')->addMethods(array('__invoke'))->getMock();
+        } else {
+            // legacy PHPUnit 4 - PHPUnit 9
+            return $this->getMockBuilder('stdClass')->setMethods(array('__invoke'))->getMock();
+        }
     }
 
     protected function expectPromiseRejected($promise)