diff --git a/lib/Signaling/Listener.php b/lib/Signaling/Listener.php
index 898522217b3..f4f552eee61 100644
--- a/lib/Signaling/Listener.php
+++ b/lib/Signaling/Listener.php
@@ -530,6 +530,7 @@ protected function notifyMessageSent(AMessageSentEvent $event): void {
 			$thread = null;
 		}
 		$data['chat']['comment'] = $message->toArray('json', $thread);
+		$data['chat']['comment']['lastCommonRead'] = $this->participantService->getLastCommonReadChatMessage($room);
 
 		$parent = $event->getParent();
 		if ($parent !== null) {
@@ -593,6 +594,7 @@ protected function notifySystemMessageSent(ASystemMessageSentEvent $event): void
 		}
 
 		$data['chat']['comment'] = $message->toArray('json', $thread);
+		$data['chat']['comment']['lastCommonRead'] = $this->participantService->getLastCommonReadChatMessage($room);
 
 		if ($messageType === 'call_started') {
 			$metaData = $comment->getMetaData() ?? [];
@@ -701,6 +703,7 @@ protected function notifyReactionSent(AReactionEvent $event): void {
 			'markdown' => false ,
 			'expirationTimestamp' => $message->getExpirationDateTime()?->getTimestamp() ?? 0,
 			'threadId' => $threadId,
+			'lastCommonRead' => $this->participantService->getLastCommonReadChatMessage($room),
 		];
 
 		$data['chat']['comment']['parent'] = $message->toArray('json', $thread);
diff --git a/tests/php/Signaling/ListenerTest.php b/tests/php/Signaling/ListenerTest.php
index 03255ced205..89e0f2e98c5 100644
--- a/tests/php/Signaling/ListenerTest.php
+++ b/tests/php/Signaling/ListenerTest.php
@@ -290,7 +290,9 @@ public function testChatMessageSentEvent(): void {
 		$comment->method('getId')->willReturn(1);
 		$message = $this->createConfiguredMock(Message::class, [
 			'getVisibility' => true,
-			'toArray' => [],
+			'toArray' => [
+				'id' => 123,
+			],
 			'getMessageId' => 123,
 		]);
 		$l10n = $this->createStub(IL10N::class);
@@ -317,7 +319,10 @@ public function testChatMessageSentEvent(): void {
 				'type' => 'chat',
 				'chat' => [
 					'refresh' => true,
-					'comment' => [],
+					'comment' => [
+						'id' => 123,
+						'lastCommonRead' => 0,
+					],
 				],
 			]);
 
@@ -333,7 +338,9 @@ public function testChatMessageSentWithThreadEvent(): void {
 		$comment->method('getId')->willReturn(1);
 		$message = $this->createConfiguredMock(Message::class, [
 			'getVisibility' => true,
-			'toArray' => [],
+			'toArray' => [
+				'id' => 123,
+			],
 			'getMessageId' => 123,
 		]);
 
@@ -365,7 +372,10 @@ public function testChatMessageSentWithThreadEvent(): void {
 				'type' => 'chat',
 				'chat' => [
 					'refresh' => true,
-					'comment' => [],
+					'comment' => [
+						'id' => 123,
+						'lastCommonRead' => 0,
+					],
 				],
 			]);