diff --git a/src/Symfony/Component/EventDispatcher/DependencyInjection/RegisterListenersPass.php b/src/Symfony/Component/EventDispatcher/DependencyInjection/RegisterListenersPass.php
index 1a52c3e865..1c4e12ec86 100644
--- a/src/Symfony/Component/EventDispatcher/DependencyInjection/RegisterListenersPass.php
+++ b/src/Symfony/Component/EventDispatcher/DependencyInjection/RegisterListenersPass.php
@@ -81,7 +81,7 @@ class RegisterListenersPass implements CompilerPassInterface
 
                 if (!isset($event['method'])) {
                     $event['method'] = 'on'.preg_replace_callback([
-                        '/(?<=\b)[a-z]/i',
+                        '/(?<=\b|_)[a-z]/i',
                         '/[^a-z0-9]/i',
                     ], function ($matches) { return strtoupper($matches[0]); }, $event['event']);
                     $event['method'] = preg_replace('/[^a-z0-9]/i', '', $event['method']);
diff --git a/src/Symfony/Component/EventDispatcher/Tests/DependencyInjection/RegisterListenersPassTest.php b/src/Symfony/Component/EventDispatcher/Tests/DependencyInjection/RegisterListenersPassTest.php
index c4623bdbcb..e0afe2c72b 100644
--- a/src/Symfony/Component/EventDispatcher/Tests/DependencyInjection/RegisterListenersPassTest.php
+++ b/src/Symfony/Component/EventDispatcher/Tests/DependencyInjection/RegisterListenersPassTest.php
@@ -175,6 +175,7 @@ class RegisterListenersPassTest extends TestCase
         $container->register('foo', \stdClass::class)->addTag('kernel.event_listener', ['event' => 'foo.bar']);
         $container->register('bar', InvokableListenerService::class)->addTag('kernel.event_listener', ['event' => 'foo.bar']);
         $container->register('baz', InvokableListenerService::class)->addTag('kernel.event_listener', ['event' => 'event']);
+        $container->register('zar', \stdClass::class)->addTag('kernel.event_listener', ['event' => 'foo.bar_zar']);
         $container->register('event_dispatcher', \stdClass::class);
 
         $registerListenersPass = new RegisterListenersPass();
@@ -206,6 +207,14 @@ class RegisterListenersPassTest extends TestCase
                     0,
                 ],
             ],
+            [
+                'addListener',
+                [
+                    'foo.bar_zar',
+                    [new ServiceClosureArgument(new Reference('zar')), 'onFooBarZar'],
+                    0,
+                ],
+            ],
         ];
         $this->assertEquals($expectedCalls, $definition->getMethodCalls());
     }