diff --git a/DependencyInjection/Compiler/MailerCompilerPass.php b/DependencyInjection/Compiler/MailerCompilerPass.php
index 436fcaee..67950571 100644
--- a/DependencyInjection/Compiler/MailerCompilerPass.php
+++ b/DependencyInjection/Compiler/MailerCompilerPass.php
@@ -5,6 +5,7 @@
 use Symfony\Component\Config\FileLocator;
 use Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
+use Symfony\Component\DependencyInjection\Exception\ServiceNotFoundException;
 use Symfony\Component\DependencyInjection\Loader;
 
 /**
@@ -22,11 +23,12 @@ public function process(ContainerBuilder $container)
             return;
         }
 
-        if (!$container->hasDefinition('mailer')) {
+        try {
+            $definition = $container->findDefinition('mailer');
+        } catch (ServiceNotFoundException $e) {
             throw new \InvalidArgumentException('To enable mail reporting you have to install the "swiftmailer/swiftmailer" or "symfony/mailer".');
         }
 
-        $definition = $container->getDefinition('mailer');
         $filename = \Swift_Mailer::class !== $definition->getClass() ? 'symfony_mailer.xml' : 'swift_mailer.xml';
 
         $loader = new Loader\XmlFileLoader($container, new FileLocator(__DIR__.'/../../Resources/config'));
diff --git a/Tests/DependencyInjection/Compiler/MailerCompilerPassTest.php b/Tests/DependencyInjection/Compiler/MailerCompilerPassTest.php
index 08cbde1b..9a85c234 100644
--- a/Tests/DependencyInjection/Compiler/MailerCompilerPassTest.php
+++ b/Tests/DependencyInjection/Compiler/MailerCompilerPassTest.php
@@ -65,6 +65,19 @@ public function testSwiftMailer()
         );
     }
 
+    public function testSwiftMailerWithAliasDefinition()
+    {
+        $this->setParameter('liip_monitor.mailer.enabled', true);
+        $this->setDefinition('swift.mailer', new Definition(\Swift_Mailer::class));
+        $this->container->setAlias('mailer', 'swift.mailer');
+
+        $this->assertContainerBuilderHasAlias('mailer');
+
+        $this->compile();
+
+        $this->assertContainerBuilderHasService('liip_monitor.reporter.swift_mailer', SwiftMailerReporter::class);
+    }
+
     public function testSymfonyMailer()
     {
         $this->setParameter('liip_monitor.mailer.enabled', true);
@@ -107,6 +120,19 @@ public function testSymfonyMailer()
         );
     }
 
+    public function testSymfonyMailerWithAliasDefinition()
+    {
+        $this->setParameter('liip_monitor.mailer.enabled', true);
+        $this->setDefinition('symfony.mailer', new Definition(MailerInterface::class));
+        $this->container->setAlias('mailer', 'symfony.mailer');
+
+        $this->assertContainerBuilderHasAlias('mailer');
+
+        $this->compile();
+
+        $this->assertContainerBuilderHasService('liip_monitor.reporter.symfony_mailer', SymfonyMailerReporter::class);
+    }
+
     public function testMailerWithoutPackage()
     {
         $this->setParameter('liip_monitor.mailer.enabled', true);
@@ -117,6 +143,19 @@ public function testMailerWithoutPackage()
         $this->compile();
     }
 
+    public function testMailerMissingAliasDefinition()
+    {
+        $this->setParameter('liip_monitor.mailer.enabled', true);
+        $this->setDefinition('swift.mailer', new Definition(\Swift_Mailer::class));
+
+        $this->assertFalse($this->container->hasAlias('mailer'));
+
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('To enable mail reporting you have to install the "swiftmailer/swiftmailer" or "symfony/mailer".');
+
+        $this->compile();
+    }
+
     protected function registerCompilerPass(ContainerBuilder $container): void
     {
         $container->addCompilerPass(new MailerCompilerPass());