diff --git a/app/config/collections.php b/app/config/collections.php
index a8965c011d..cdc5d03b8d 100644
--- a/app/config/collections.php
+++ b/app/config/collections.php
@@ -2113,6 +2113,13 @@ $commonCollections = [
                 'lengths' => [],
                 'orders' => [],
             ],
+            [
+                '$id' => ID::custom('_unique_target_topic'),
+                'type' => Database::INDEX_UNIQUE,
+                'attributes' => ['targetInternalId', 'topicInternalId'],
+                'lengths' => [],
+                'orders' => [],
+            ],
             [
                 '$id' => ID::custom('_fulltext_search'),
                 'type' => Database::INDEX_FULLTEXT,
diff --git a/tests/e2e/Services/Messaging/MessagingBase.php b/tests/e2e/Services/Messaging/MessagingBase.php
index 956ac5f68a..25bf985692 100644
--- a/tests/e2e/Services/Messaging/MessagingBase.php
+++ b/tests/e2e/Services/Messaging/MessagingBase.php
@@ -444,6 +444,17 @@ trait MessagingBase
         $this->assertEquals($target['body']['userId'], $response['body']['target']['userId']);
         $this->assertEquals($target['body']['providerType'], $response['body']['target']['providerType']);
 
+        // Test duplicate subscribers not allowed
+        $failure = $this->client->call(Client::METHOD_POST, '/messaging/topics/' . $topics['public']['$id'] . '/subscribers', \array_merge([
+            'content-type' => 'application/json',
+            'x-appwrite-project' => $this->getProject()['$id'],
+        ], $this->getHeaders()), [
+            'subscriberId' => ID::unique(),
+            'targetId' => $target['body']['$id'],
+        ]);
+
+        $this->assertEquals(409, $failure['headers']['status-code']);
+
         $topic = $this->client->call(Client::METHOD_GET, '/messaging/topics/' . $topics['public']['$id'], [
             'content-type' => 'application/json',
             'x-appwrite-project' => $this->getProject()['$id'],