symfony
diff --git a/‎src/Symfony/Component/Messenger/DependencyInjection/MessengerPass.php
Lines changed: 6 additions & 1 deletion b/‎src/Symfony/Component/Messenger/DependencyInjection/MessengerPass.php
Lines changed: 6 additions & 1 deletion
diff --git a/‎src/Symfony/Component/Messenger/Tests/DependencyInjection/MessengerPassTest.php
Lines changed: 16 additions & 0 deletions b/‎src/Symfony/Component/Messenger/Tests/DependencyInjection/MessengerPassTest.php
Lines changed: 16 additions & 0 deletions
@@ -79,7 +79,12 @@ private function registerHandlers(ContainerBuilder $container, array $busIds)
                     throw new RuntimeException(sprintf('Invalid handler service "%s": bus "%s" specified on the tag "%s" does not exist (known ones are: %s).', $serviceId, $tag['bus'], $this->handlerTag, implode(', ', $busIds)));
                 }
 
-                $r = $container->getReflectionClass($container->getDefinition($serviceId)->getClass());
+                $className = $container->getDefinition($serviceId)->getClass();
+                $r = $container->getReflectionClass($className);
+
+                if (null === $r) {
+                    throw new RuntimeException(sprintf('Invalid service "%s": class "%s" does not exist.', $serviceId, $className));
+                }
 
                 if (isset($tag['handles'])) {
                     $handles = isset($tag['method']) ? array($tag['handles'] => $tag['method']) : array($tag['handles']);
 
@@ -194,6 +194,22 @@ public function testGetClassesAndMethodsAndPrioritiesFromTheSubscriber()
         $this->assertSame(PrioritizedHandler::class, $secondHandlerDefinition->getClass());
     }
 
+    /**
+     * @expectedException \Symfony\Component\DependencyInjection\Exception\RuntimeException
+     * @expectedExceptionMessage Invalid service "NonExistentHandlerClass": class "NonExistentHandlerClass" does not exist.
+     */
+    public function testThrowsExceptionIfTheHandlerClassDoesNotExist()
+    {
+        $container = $this->getContainerBuilder();
+        $container->register('message_bus', MessageBusInterface::class)->addTag('messenger.bus');
+        $container
+            ->register('NonExistentHandlerClass', 'NonExistentHandlerClass')
+            ->addTag('messenger.message_handler')
+        ;
+
+        (new MessengerPass())->process($container);
+    }
+
     /**
      * @expectedException \Symfony\Component\DependencyInjection\Exception\RuntimeException
      * @expectedExceptionMessage Invalid handler service "Symfony\Component\Messenger\Tests\DependencyInjection\HandlerMappingWithNonExistentMethod": method "Symfony\Component\Messenger\Tests\DependencyInjection\HandlerMappingWithNonExistentMethod::dummyMethod()" does not exist.