diff --git a/composer.json b/composer.json
index 4871a35e6..d22ff95e2 100644
--- a/composer.json
+++ b/composer.json
@@ -21,9 +21,10 @@
         "ext-mbstring": "*",
         "jean85/pretty-package-versions": "^1.2",
         "php-http/async-client-implementation": "^1.0",
-        "php-http/client-common": "^1.5",
-        "php-http/discovery": "^1.2",
-        "php-http/httplug": "^1.1",
+        "php-http/client-common": "^1.5|^2.0",
+        "php-http/discovery": "^1.6.1",
+        "php-http/httplug": "^1.1|^2.0",
+        "php-http/message": "^1.5",
         "psr/http-message-implementation": "^1.0",
         "ramsey/uuid": "^3.3",
         "symfony/options-resolver": "^2.7|^3.0|^4.0",
@@ -32,8 +33,6 @@
     "require-dev": {
         "friendsofphp/php-cs-fixer": "^2.13",
         "monolog/monolog": "^1.3",
-        "php-http/curl-client": "^1.7.1",
-        "php-http/message": "^1.5",
         "php-http/mock-client": "^1.0",
         "phpstan/phpstan-phpunit": "^0.10",
         "phpstan/phpstan": "^0.10.3",
diff --git a/phpstan.neon b/phpstan.neon
index 44470014f..e6714eab8 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -8,6 +8,7 @@ parameters:
         - '/Argument of an invalid type object supplied for foreach, only iterables are supported/'
         - '/Binary operation "\*" between array and 2 results in an error\./'
         - '/Method Sentry\\Serializer\\RepresentationSerializer::(representationSerialize|serializeValue)\(\) should return [\w|]+ but returns [\w|]+/'
+        - '/Http\\Client\\Curl\\Client/'
     excludes_analyse:
         - tests/resources
 includes:
diff --git a/src/ClientBuilder.php b/src/ClientBuilder.php
index 33ab7c922..eb440736a 100644
--- a/src/ClientBuilder.php
+++ b/src/ClientBuilder.php
@@ -14,6 +14,7 @@
 use Http\Client\Common\PluginClient;
 use Http\Client\Curl\Client as HttpCurlClient;
 use Http\Client\HttpAsyncClient;
+use Http\Discovery\ClassDiscovery;
 use Http\Discovery\HttpAsyncClientDiscovery;
 use Http\Discovery\MessageFactoryDiscovery;
 use Http\Discovery\UriFactoryDiscovery;
@@ -321,13 +322,13 @@ private function createTransportInstance(): TransportInterface
                 throw new \RuntimeException('The `http_proxy` option does not work together with a custom client.');
             }
 
-            if (HttpAsyncClientDiscovery::safeClassExists(HttpCurlClient::class)) {
-                $this->httpClient = new HttpCurlClient(null, null, [
-                    CURLOPT_PROXY => $this->options->getHttpProxy(),
-                ]);
-            } else {
+            if (!ClassDiscovery::safeClassExists(HttpCurlClient::class)) {
                 throw new \RuntimeException('The `http_proxy` option requires the `php-http/curl-client` package to be installed.');
             }
+
+            $this->httpClient = new HttpCurlClient(null, null, [
+                CURLOPT_PROXY => $this->options->getHttpProxy(),
+            ]);
         }
 
         $this->httpClient = $this->httpClient ?? HttpAsyncClientDiscovery::find();
diff --git a/tests/ClientBuilderTest.php b/tests/ClientBuilderTest.php
index 9dad066f5..984b0ca14 100644
--- a/tests/ClientBuilderTest.php
+++ b/tests/ClientBuilderTest.php
@@ -9,6 +9,7 @@
 use Http\Client\HttpAsyncClient;
 use Http\Message\MessageFactory;
 use Http\Message\UriFactory;
+use Http\Promise\Promise;
 use Jean85\PrettyVersions;
 use PHPUnit\Framework\MockObject\MockObject;
 use PHPUnit\Framework\TestCase;
@@ -317,14 +318,14 @@ public function setupOnce(): void
 
 final class PluginStub1 implements Plugin
 {
-    public function handleRequest(RequestInterface $request, callable $next, callable $first)
+    public function handleRequest(RequestInterface $request, callable $next, callable $first): Promise
     {
     }
 }
 
 final class PluginStub2 implements Plugin
 {
-    public function handleRequest(RequestInterface $request, callable $next, callable $first)
+    public function handleRequest(RequestInterface $request, callable $next, callable $first): Promise
     {
     }
 }
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
index 57982bce2..166f1c4ba 100644
--- a/tests/bootstrap.php
+++ b/tests/bootstrap.php
@@ -2,8 +2,13 @@
 
 declare(strict_types=1);
 
+use Http\Discovery\ClassDiscovery;
+use Http\Discovery\Strategy\MockClientStrategy;
+
 error_reporting(E_ALL | E_STRICT);
 
 session_start();
 
 require_once __DIR__ . '/../vendor/autoload.php';
+
+ClassDiscovery::appendStrategy(MockClientStrategy::class);
diff --git a/tests/phpt/fatal_error.phpt b/tests/phpt/fatal_error.phpt
index 4d040c05f..4f8539179 100644
--- a/tests/phpt/fatal_error.phpt
+++ b/tests/phpt/fatal_error.phpt
@@ -17,10 +17,7 @@ while (!file_exists($vendor . '/vendor')) {
 
 require $vendor . '/vendor/autoload.php';
 
-init([
-    'dsn' => 'http://public:secret@local.host/1',
-    'send_attempts' => 1,
-]);
+init();
 
 ErrorHandler::addErrorListener(new StubErrorListener(function () {
     echo 'Listener called';
diff --git a/tests/phpt/out_of_memory.phpt b/tests/phpt/out_of_memory.phpt
index 151cddbfb..ded7b8718 100644
--- a/tests/phpt/out_of_memory.phpt
+++ b/tests/phpt/out_of_memory.phpt
@@ -6,8 +6,9 @@ Test catching out of memory fatal error
 namespace Sentry\Tests;
 
 use PHPUnit\Framework\Assert;
+use Sentry\Event;
+use Sentry\Severity;
 use function Sentry\init;
-use Sentry\State\Hub;
 
 ini_set('memory_limit', '20M');
 
@@ -20,23 +21,20 @@ while (!file_exists($vendor . '/vendor')) {
 require $vendor . '/vendor/autoload.php';
 
 init([
-    'dsn' => 'http://public:secret@local.host/1',
-    'send_attempts' => 1,
-]);
-
-register_shutdown_function('register_shutdown_function', function () {
-    $client = Hub::getCurrent()->getClient();
+    'before_send' => function (Event $event): ?Event {
+        Assert::assertArrayHasKey(0,  $event->getExceptions());
+        $error = $event->getExceptions()[0];
+        Assert::assertContains('Allowed memory size', $error['value']);
+        Assert::assertTrue($event->getLevel()->isEqualTo(Severity::fatal()));
 
-    /** @var \Sentry\Transport\HttpTransport $transport */
-    $transport = Assert::getObjectAttribute($client, 'transport');
+        echo 'Sending event';
 
-    Assert::assertAttributeEmpty('pendingRequests', $transport);
-
-    echo 'Shutdown function called';
-});
+        return null;
+    },
+]);
 
 $foo = str_repeat('x', 1024 * 1024 * 30);
 ?>
 --EXPECTF--
 Fatal error: Allowed memory size of %d bytes exhausted (tried to allocate %d bytes) in %s on line %d
-Shutdown function called
+Sending event