diff --git a/lib/Federation/Proxy/TalkV1/Controller/ChatController.php b/lib/Federation/Proxy/TalkV1/Controller/ChatController.php
index 4ceb5a4a311..a601166d14b 100644
--- a/lib/Federation/Proxy/TalkV1/Controller/ChatController.php
+++ b/lib/Federation/Proxy/TalkV1/Controller/ChatController.php
@@ -371,14 +371,14 @@ public function deleteMessage(Room $room, Participant $participant, int $message
 	 *
 	 * 200: List of mention suggestions returned
 	 */
-	public function setReadMarker(Room $room, Participant $participant, string $responseFormat, int $lastReadMessage): DataResponse {
+	public function setReadMarker(Room $room, Participant $participant, string $responseFormat, ?int $lastReadMessage): DataResponse {
 		$proxy = $this->proxy->post(
 			$participant->getAttendee()->getInvitedCloudId(),
 			$participant->getAttendee()->getAccessToken(),
 			$room->getRemoteServer() . '/ocs/v2.php/apps/spreed/api/v1/chat/' . $room->getRemoteToken() . '/read',
-			[
+			$lastReadMessage !== null ? [
 				'lastReadMessage' => $lastReadMessage,
-			],
+			] : [],
 		);
 
 		/** @var TalkRoom $data */
diff --git a/tests/integration/features/federation/chat.feature b/tests/integration/features/federation/chat.feature
index 0849772cd0f..0c12fb3f0a2 100644
--- a/tests/integration/features/federation/chat.feature
+++ b/tests/integration/features/federation/chat.feature
@@ -126,6 +126,48 @@ Feature: federation/chat
       | room | users           | participant2             | participant2-displayname | Message deleted by you    | {"actor":{"type":"user","id":"participant2","name":"participant2-displayname"}}                        | Message deleted by author |
       | room | federated_users | participant1@{$BASE_URL} | participant1-displayname | Message deleted by author | {"actor":{"type":"user","id":"participant1","name":"participant1-displayname","server":"{$BASE_URL}"}} |                           |
 
+  Scenario: Read marker checking
+    Given the following "spreed" app config is set
+      | federation_enabled | yes |
+    Given user "participant1" creates room "room" (v4)
+      | roomType | 2 |
+      | roomName | room |
+    And user "participant1" adds federated_user "participant2" to room "room" with 200 (v4)
+    And user "participant1" adds federated_user "participant3" to room "room" with 200 (v4)
+    And user "participant2" has the following invitations (v1)
+      | remoteServerUrl | remoteToken | state | inviterCloudId                     | inviterDisplayName       |
+      | LOCAL           | room        | 0     | participant1@http://localhost:8080 | participant1-displayname |
+    And user "participant2" accepts invite to room "room" of server "LOCAL" with 200 (v1)
+      | id   | name | type | remoteServer | remoteToken |
+      | room | room | 2    | LOCAL        | room        |
+    And user "participant3" has the following invitations (v1)
+      | remoteServerUrl | remoteToken | state | inviterCloudId                     | inviterDisplayName       |
+      | LOCAL           | room        | 0     | participant1@http://localhost:8080 | participant1-displayname |
+    And user "participant3" accepts invite to room "room" of server "LOCAL" with 200 (v1)
+      | id   | name | type | remoteServer | remoteToken |
+      | room | room | 2    | LOCAL        | room        |
+    Then user "participant2" is participant of the following rooms (v4)
+      | id   | type | unreadMessages | unreadMention | unreadMentionDirect |
+      | room | 2    | 0              | 0             | 0                   |
+    And user "participant1" sends message "Message 1" to room "room" with 201
+    And user "participant1" sends message "Message 2" to room "room" with 201
+    When user "participant2" marks room "LOCAL::room" as unread with 200 (v1)
+    Then user "participant2" is participant of the following rooms (v4)
+      | id   | type | unreadMessages | unreadMention | unreadMentionDirect |
+      | room | 2    | 1              | 0             | 0                   |
+    When user "participant2" reads message "NULL" in room "LOCAL::room" with 200 (v1)
+    Then user "participant2" is participant of the following rooms (v4)
+      | id   | type | unreadMessages | unreadMention | unreadMentionDirect |
+      | room | 2    | 0              | 0             | 0                   |
+    When user "participant2" reads message "Message 1" in room "LOCAL::room" with 200 (v1)
+    Then user "participant2" is participant of the following rooms (v4)
+      | id   | type | unreadMessages | unreadMention | unreadMentionDirect |
+      | room | 2    | 1              | 0             | 0                   |
+    When user "participant2" reads message "Message 2" in room "LOCAL::room" with 200 (v1)
+    Then user "participant2" is participant of the following rooms (v4)
+      | id   | type | unreadMessages | unreadMention | unreadMentionDirect |
+      | room | 2    | 0              | 0             | 0                   |
+
   Scenario: Error handling of chatting (posting a too long message)
     Given the following "spreed" app config is set
       | federation_enabled | yes |