diff --git a/src/Symfony/Bundle/FrameworkBundle/DependencyInjection/FrameworkExtension.php b/src/Symfony/Bundle/FrameworkBundle/DependencyInjection/FrameworkExtension.php
index d8f4b61699a9e..dafdc40219f95 100644
--- a/src/Symfony/Bundle/FrameworkBundle/DependencyInjection/FrameworkExtension.php
+++ b/src/Symfony/Bundle/FrameworkBundle/DependencyInjection/FrameworkExtension.php
@@ -277,6 +277,7 @@ public function load(array $configs, ContainerBuilder $container)
             $this->registerMessengerConfiguration($config['messenger'], $container, $loader, $config['serializer'], $config['validation']);
         } else {
             $container->removeDefinition('console.command.messenger_consume_messages');
+            $container->removeDefinition('console.command.messenger_debug');
         }
 
         if ($this->isConfigEnabled($container, $config['web_link'])) {
diff --git a/src/Symfony/Bundle/FrameworkBundle/Resources/config/console.xml b/src/Symfony/Bundle/FrameworkBundle/Resources/config/console.xml
index cb71bbb8de8f7..21fe28375f6fb 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Resources/config/console.xml
+++ b/src/Symfony/Bundle/FrameworkBundle/Resources/config/console.xml
@@ -77,6 +77,11 @@
             <tag name="console.command" command="messenger:consume-messages" />
         </service>
 
+        <service id="console.command.messenger_debug" class="Symfony\Component\Messenger\Command\DebugCommand">
+            <argument type="collection" /> <!-- Message to handlers mapping -->
+            <tag name="console.command" command="debug:messenger" />
+        </service>
+
         <service id="console.command.router_debug" class="Symfony\Bundle\FrameworkBundle\Command\RouterDebugCommand">
             <argument type="service" id="router" />
             <tag name="console.command" command="debug:router" />
diff --git a/src/Symfony/Bundle/FrameworkBundle/composer.json b/src/Symfony/Bundle/FrameworkBundle/composer.json
index 8c1c32194fdea..3dfca6a069709 100644
--- a/src/Symfony/Bundle/FrameworkBundle/composer.json
+++ b/src/Symfony/Bundle/FrameworkBundle/composer.json
@@ -41,7 +41,7 @@
         "symfony/security": "~3.4|~4.0",
         "symfony/form": "^4.1",
         "symfony/expression-language": "~3.4|~4.0",
-        "symfony/messenger": "^4.1",
+        "symfony/messenger": "^4.1-beta2",
         "symfony/process": "~3.4|~4.0",
         "symfony/security-core": "~3.4|~4.0",
         "symfony/security-csrf": "~3.4|~4.0",
diff --git a/src/Symfony/Component/Messenger/Command/DebugCommand.php b/src/Symfony/Component/Messenger/Command/DebugCommand.php
new file mode 100644
index 0000000000000..f41747dc0f649
--- /dev/null
+++ b/src/Symfony/Component/Messenger/Command/DebugCommand.php
@@ -0,0 +1,81 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Messenger\Command;
+
+use Symfony\Component\Console\Command\Command;
+use Symfony\Component\Console\Input\InputInterface;
+use Symfony\Component\Console\Output\OutputInterface;
+use Symfony\Component\Console\Style\SymfonyStyle;
+
+/**
+ * A console command to debug Messenger information.
+ *
+ * @author Roland Franssen <franssen.roland@gmail.com>
+ *
+ * @experimental in 4.1
+ */
+class DebugCommand extends Command
+{
+    protected static $defaultName = 'debug:messenger';
+
+    private $mapping;
+
+    public function __construct(array $mapping)
+    {
+        parent::__construct();
+
+        $this->mapping = $mapping;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function configure()
+    {
+        $this
+            ->setDescription('Lists messages you can dispatch using the message bus')
+            ->setHelp(<<<'EOF'
+The <info>%command.name%</info> command displays all messages that can be
+dispatched using the message bus:
+
+  <info>php %command.full_name%</info>
+
+EOF
+            )
+        ;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function execute(InputInterface $input, OutputInterface $output)
+    {
+        $io = new SymfonyStyle($input, $output);
+        $io->title('Messenger');
+        $io->text('The following messages can be dispatched:');
+        $io->newLine();
+
+        $tableRows = array();
+        foreach ($this->mapping as $message => $handlers) {
+            $tableRows[] = array(sprintf('<fg=cyan>%s</fg=cyan>', $message));
+            foreach ($handlers as $handler) {
+                $tableRows[] = array(sprintf('    handled by %s', $handler));
+            }
+        }
+
+        if ($tableRows) {
+            $io->table(array(), $tableRows);
+        } else {
+            $io->text('No messages were found that have valid handlers.');
+        }
+    }
+}
diff --git a/src/Symfony/Component/Messenger/DependencyInjection/MessengerPass.php b/src/Symfony/Component/Messenger/DependencyInjection/MessengerPass.php
index 1fd76db8fee25..2af6577f485a8 100644
--- a/src/Symfony/Component/Messenger/DependencyInjection/MessengerPass.php
+++ b/src/Symfony/Component/Messenger/DependencyInjection/MessengerPass.php
@@ -104,26 +104,29 @@ private function registerHandlers(ContainerBuilder $container)
         }
 
         $definitions = array();
+        $handlersLocatorMapping = array();
         foreach ($handlersByMessage as $message => $handlers) {
             if (1 === \count($handlers)) {
-                $handlersByMessage[$message] = current($handlers);
+                $handlersLocatorMapping['handler.'.$message] = current($handlers);
             } else {
                 $d = new Definition(ChainHandler::class, array($handlers));
                 $d->setPrivate(true);
                 $serviceId = hash('sha1', $message);
                 $definitions[$serviceId] = $d;
-                $handlersByMessage[$message] = new Reference($serviceId);
+                $handlersLocatorMapping['handler.'.$message] = new Reference($serviceId);
             }
         }
         $container->addDefinitions($definitions);
 
-        $handlersLocatorMapping = array();
-        foreach ($handlersByMessage as $message => $handler) {
-            $handlersLocatorMapping['handler.'.$message] = $handler;
-        }
-
         $handlerResolver = $container->getDefinition('messenger.handler_resolver');
         $handlerResolver->replaceArgument(0, ServiceLocatorTagPass::register($container, $handlersLocatorMapping));
+
+        if ($container->hasDefinition('console.command.messenger_debug')) {
+            $container->getDefinition('console.command.messenger_debug')
+                ->replaceArgument(0, array_map(function (array $handlers): array {
+                    return array_map('strval', $handlers);
+                }, $handlersByMessage));
+        }
     }
 
     private function guessHandledClasses(\ReflectionClass $handlerClass, string $serviceId): array