diff --git a/DependencyInjection/HttplugExtension.php b/DependencyInjection/HttplugExtension.php
index e8afe492..1a010185 100644
--- a/DependencyInjection/HttplugExtension.php
+++ b/DependencyInjection/HttplugExtension.php
@@ -14,6 +14,7 @@
 use Http\Message\Authentication\Wsse;
 use Psr\Http\Message\UriInterface;
 use Symfony\Component\Config\FileLocator;
+use Symfony\Component\DependencyInjection\Alias;
 use Symfony\Component\DependencyInjection\ChildDefinition;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
 use Symfony\Component\DependencyInjection\Definition;
@@ -50,7 +51,7 @@ public function load(array $configs, ContainerBuilder $container)
 
         // Set main aliases
         foreach ($config['main_alias'] as $type => $id) {
-            $container->setAlias(sprintf('httplug.%s', $type), $id);
+            $container->setAlias(sprintf('httplug.%s', $type), new Alias($id, true));
         }
 
         // Configure toolbar
@@ -103,7 +104,7 @@ private function configureClients(ContainerBuilder $container, array $config)
             // If we do not have a client named 'default'
             if (!isset($config['clients']['default'])) {
                 // Alias the first client to httplug.client.default
-                $container->setAlias('httplug.client.default', 'httplug.client.'.$first);
+                $container->setAlias('httplug.client.default', new Alias('httplug.client.'.$first, true));
             }
         }
     }
@@ -297,6 +298,7 @@ private function configureClient(ContainerBuilder $container, $clientName, array
 
         $container
             ->register($serviceId, PluginClient::class)
+            ->setPublic(true)
             ->setFactory([new Reference(PluginClientFactory::class), 'createClient'])
             ->addArgument(new Reference($serviceId.'.client'))
             ->addArgument(
diff --git a/Resources/config/services.xml b/Resources/config/services.xml
index 194921b8..89738ab3 100644
--- a/Resources/config/services.xml
+++ b/Resources/config/services.xml
@@ -4,44 +4,44 @@
            xsi:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd">
 
     <services>
-        <service id="httplug.strategy" class="Http\HttplugBundle\Discovery\ConfiguredClientsStrategy">
+        <service id="httplug.strategy" class="Http\HttplugBundle\Discovery\ConfiguredClientsStrategy" public="true">
             <argument type="service" id="httplug.auto_discovery.auto_discovered_client" on-invalid="null"/>
             <argument type="service" id="httplug.auto_discovery.auto_discovered_async" on-invalid="null"/>
             <tag name="kernel.event_subscriber"/>
         </service>
 
-        <service id="httplug.auto_discovery.auto_discovered_client" class="Http\Client\HttpClient">
+        <service id="httplug.auto_discovery.auto_discovered_client" class="Http\Client\HttpClient" public="true">
             <factory class="Http\Discovery\HttpClientDiscovery" method="find" />
         </service>
 
-        <service id="httplug.auto_discovery.auto_discovered_async" class="Http\Client\HttpAsyncClient">
+        <service id="httplug.auto_discovery.auto_discovered_async" class="Http\Client\HttpAsyncClient" public="true">
             <factory class="Http\Discovery\HttpAsyncClientDiscovery" method="find" />
         </service>
 
         <!-- Discovery with autowiring support for Symfony 3.3+ -->
-        <service id="httplug.message_factory.default" class="Http\Message\MessageFactory">
+        <service id="httplug.message_factory.default" class="Http\Message\MessageFactory" public="true">
             <factory class="Http\Discovery\MessageFactoryDiscovery" method="find" />
         </service>
         <service id="Http\Message\MessageFactory" alias="httplug.message_factory" public="false" />
         <service id="Http\Message\RequestFactory" alias="httplug.message_factory" public="false" />
         <service id="Http\Message\ResponseFactory" alias="httplug.message_factory" public="false" />
 
-        <service id="httplug.stream_factory.default" class="Http\Message\StreamFactory">
+        <service id="httplug.stream_factory.default" class="Http\Message\StreamFactory" public="true">
             <factory class="Http\Discovery\StreamFactoryDiscovery" method="find" />
         </service>
         <service id="Http\Message\StreamFactory" alias="httplug.stream_factory" public="false" />
 
-        <service id="httplug.uri_factory.default" class="Http\Message\UriFactory">
+        <service id="httplug.uri_factory.default" class="Http\Message\UriFactory" public="true">
             <factory class="Http\Discovery\UriFactoryDiscovery" method="find" />
         </service>
         <service id="Http\Message\UriFactory" alias="httplug.uri_factory" public="false" />
 
-        <service id="httplug.async_client.default" class="Http\Client\HttpAsyncClient">
+        <service id="httplug.async_client.default" class="Http\Client\HttpAsyncClient" public="true">
             <factory class="Http\Discovery\HttpAsyncClientDiscovery" method="find" />
         </service>
         <service id="Http\Client\HttpAsyncClient" alias="httplug.async_client.default" public="false" />
 
-        <service id="httplug.client.default" class="Http\Client\HttpClient">
+        <service id="httplug.client.default" class="Http\Client\HttpClient" public="true">
             <factory class="Http\Discovery\HttpClientDiscovery" method="find" />
         </service>
         <service id="Http\Client\HttpClient" alias="httplug.client" public="false" />
diff --git a/Tests/Resources/app/config/config_test.yml b/Tests/Resources/app/config/config_test.yml
index 52288d6f..599b062a 100644
--- a/Tests/Resources/app/config/config_test.yml
+++ b/Tests/Resources/app/config/config_test.yml
@@ -26,3 +26,6 @@ httplug:
 services:
     app.http.plugin.custom:
         class: Http\Client\Common\Plugin\RedirectPlugin
+        public: true
+        # plugin services usually do not need to be public.
+        # this one is made public so that we can do functional tests on the service
diff --git a/composer.json b/composer.json
index 887d7365..d34deb7c 100644
--- a/composer.json
+++ b/composer.json
@@ -23,14 +23,14 @@
         "php-http/cache-plugin": "^1.4",
         "php-http/logger-plugin": "^1.0",
         "php-http/stopwatch-plugin": "^1.0",
-        "symfony/options-resolver": "^2.8 || ^3.0",
-        "symfony/event-dispatcher": "^2.8 || ^3.0",
-        "symfony/framework-bundle": "^2.8 || ^3.0",
+        "symfony/options-resolver": "^2.8 || ^3.0 || ^4.0",
+        "symfony/event-dispatcher": "^2.8 || ^3.0 || ^4.0",
+        "symfony/framework-bundle": "^2.8 || ^3.0 || ^4.0",
         "php-http/message": "^1.4",
         "php-http/discovery": "^1.0",
         "twig/twig": "^1.18 || ^2.0",
-        "symfony/asset": "^2.8 || ^3.0",
-        "symfony/dependency-injection": "^2.8.3 || ^3.0.3"
+        "symfony/asset": "^2.8 || ^3.0 || ^4.0",
+        "symfony/dependency-injection": "^2.8.3 || ^3.0.3 || ^4.0"
     },
     "require-dev": {
         "phpunit/php-token-stream": "^1.1.8",
@@ -41,13 +41,13 @@
         "php-http/buzz-adapter": "^0.3",
         "php-http/mock-client": "^1.0",
         "symfony/phpunit-bridge": "^3.3 || ^4.0",
-        "symfony/twig-bundle": "^2.8 || ^3.0",
-        "symfony/twig-bridge": "^2.8 || ^3.0",
-        "symfony/web-profiler-bundle": "^2.8 || ^3.0",
-        "symfony/finder": "^2.7 || ^3.0",
-        "symfony/cache": "^3.1",
-        "symfony/browser-kit": "^2.8 || ^3.0",
-        "symfony/dom-crawler": "^2.8 || ^3.0",
+        "symfony/twig-bundle": "^2.8 || ^3.0 || ^4.0",
+        "symfony/twig-bridge": "^2.8 || ^3.0 || ^4.0",
+        "symfony/web-profiler-bundle": "^2.8 || ^3.0 || ^4.0",
+        "symfony/finder": "^2.7 || ^3.0 || ^4.0",
+        "symfony/cache": "^3.1 || ^4.0",
+        "symfony/browser-kit": "^2.8 || ^3.0 || ^4.0",
+        "symfony/dom-crawler": "^2.8 || ^3.0 || ^4.0",
         "polishsymfonycommunity/symfony-mocker-container": "^1.0",
         "matthiasnoback/symfony-dependency-injection-test": "^1.1 || ^2.0",
         "nyholm/nsa": "^1.1"