diff --git a/src/Symfony/Component/Mailer/Bridge/Sendgrid/RemoteEvent/SendgridPayloadConverter.php b/src/Symfony/Component/Mailer/Bridge/Sendgrid/RemoteEvent/SendgridPayloadConverter.php
index f10e147647f2b..c73ffea03c479 100644
--- a/src/Symfony/Component/Mailer/Bridge/Sendgrid/RemoteEvent/SendgridPayloadConverter.php
+++ b/src/Symfony/Component/Mailer/Bridge/Sendgrid/RemoteEvent/SendgridPayloadConverter.php
@@ -51,7 +51,7 @@ public function convert(array $payload): AbstractMailerEvent
         $event->setDate($date);
         $event->setRecipientEmail($payload['email']);
         $event->setMetadata([]);
-        $event->setTags($payload['category'] ?? []);
+        $event->setTags((array) ($payload['category'] ?? []));
 
         return $event;
     }
diff --git a/src/Symfony/Component/Mailer/Bridge/Sendgrid/Tests/RemoteEvent/SendgridPayloadConverterTest.php b/src/Symfony/Component/Mailer/Bridge/Sendgrid/Tests/RemoteEvent/SendgridPayloadConverterTest.php
index f7201b373aa86..02811744468e3 100644
--- a/src/Symfony/Component/Mailer/Bridge/Sendgrid/Tests/RemoteEvent/SendgridPayloadConverterTest.php
+++ b/src/Symfony/Component/Mailer/Bridge/Sendgrid/Tests/RemoteEvent/SendgridPayloadConverterTest.php
@@ -112,4 +112,20 @@ public function testAsynchronousBounce()
         $this->assertInstanceOf(MailerDeliveryEvent::class, $event);
         $this->assertSame('123456', $event->getId());
     }
+
+    public function testWithStringCategory()
+    {
+        $converter = new SendgridPayloadConverter();
+
+        $event = $converter->convert([
+            'event' => 'processed',
+            'sg_message_id' => '123456',
+            'timestamp' => '123456789',
+            'email' => 'test@example.com',
+            'category' => 'cat facts',
+        ]);
+
+        $this->assertInstanceOf(MailerDeliveryEvent::class, $event);
+        $this->assertSame(['cat facts'], $event->getTags());
+    }
 }