diff --git a/src/Symfony/Bridge/Twig/Mime/NotificationEmail.php b/src/Symfony/Bridge/Twig/Mime/NotificationEmail.php
index 1a58aa5e5e5bc..382928a982da2 100644
--- a/src/Symfony/Bridge/Twig/Mime/NotificationEmail.php
+++ b/src/Symfony/Bridge/Twig/Mime/NotificationEmail.php
@@ -210,7 +210,7 @@ private function getExceptionAsString($exception): string
      */
     public function __serialize(): array
     {
-        return [$this->context, parent::__serialize()];
+        return [$this->context, $this->theme, parent::__serialize()];
     }
 
     /**
@@ -218,7 +218,12 @@ public function __serialize(): array
      */
     public function __unserialize(array $data): void
     {
-        [$this->context, $parentData] = $data;
+        if (3 === \count($data)) {
+            [$this->context, $this->theme, $parentData] = $data;
+        } else {
+            // Backwards compatibility for deserializing data structures that were serialized without the theme
+            [$this->context, $parentData] = $data;
+        }
 
         parent::__unserialize($parentData);
     }
diff --git a/src/Symfony/Bridge/Twig/Tests/Mime/NotificationEmailTest.php b/src/Symfony/Bridge/Twig/Tests/Mime/NotificationEmailTest.php
index 6c5b4a4bf579e..0b55ca01d6b3e 100644
--- a/src/Symfony/Bridge/Twig/Tests/Mime/NotificationEmailTest.php
+++ b/src/Symfony/Bridge/Twig/Tests/Mime/NotificationEmailTest.php
@@ -46,6 +46,7 @@ public function testSerialize()
             ->importance(NotificationEmail::IMPORTANCE_HIGH)
             ->action('Bar', 'http://example.com/')
             ->context(['a' => 'b'])
+            ->theme('example')
         ));
         $this->assertEquals([
             'importance' => NotificationEmail::IMPORTANCE_HIGH,
@@ -57,6 +58,8 @@ public function testSerialize()
             'raw' => true,
             'a' => 'b',
         ], $email->getContext());
+
+        $this->assertSame('@email/example/notification/body.html.twig', $email->getHtmlTemplate());
     }
 
     public function testTheme()