diff --git a/lib/Dashboard/TalkWidget.php b/lib/Dashboard/TalkWidget.php
index 373457413b9..7987f54ae05 100644
--- a/lib/Dashboard/TalkWidget.php
+++ b/lib/Dashboard/TalkWidget.php
@@ -169,7 +169,7 @@ public function getItems(string $userId, ?string $since = null, int $limit = 7):
 			}
 
 			if (($room->isFederatedConversation() && $attendee->getLastMentionMessage())
-				|| (!$room->isFederatedConversation() && $attendee->getLastMentionMessage() > $attendee->getLastReadMessage())) {
+				|| (!$room->isFederatedConversation() && $this->hasUnreadMention($attendee))) {
 				return true;
 			}
 
@@ -226,7 +226,7 @@ public function getItemsV2(string $userId, ?string $since = null, int $limit = 7
 			}
 
 			if (($room->isFederatedConversation() && $attendee->getLastMentionMessage())
-				|| (!$room->isFederatedConversation() && $attendee->getLastMentionMessage() > $attendee->getLastReadMessage())) {
+				|| (!$room->isFederatedConversation() && $this->hasUnreadMention($attendee))) {
 				// Really mentioned
 				$mentions[] = $room;
 				continue;
@@ -290,7 +290,7 @@ protected function prepareRoom(Room $room, string $userId): WidgetItem {
 			}
 		} elseif ($room->getLastMessageId() && $room->getLastMessage() && !$room->isFederatedConversation()) {
 			$comment = $room->getLastMessage();
-			if ($attendee->getLastMentionMessage() > $attendee->getLastReadMessage()) {
+			if ($this->hasUnreadMention($attendee)) {
 				// Last mention is unread, show that instead
 				try {
 					$comment = $this->chatManager->getComment($room, (string)$attendee->getLastMentionMessage());
@@ -334,6 +334,15 @@ protected function getSubtitleFromMessage(Message $message): string {
 		return str_replace($placeholders, $replacements, $message->getMessage());
 	}
 
+	/**
+	 * last_mention_message is 0 when there is no mention, while last_read_message
+	 * can be negative ({@see ChatManager::UNREAD_FIRST_MESSAGE}, {@see ChatManager::UNREAD_MIGRATION}).
+	 */
+	protected function hasUnreadMention(Attendee $attendee): bool {
+		$lastMention = $attendee->getLastMentionMessage();
+		return $lastMention > 0 && $lastMention > $attendee->getLastReadMessage();
+	}
+
 	protected function sortRooms(Room $roomA, Room $roomB): int {
 		if ($roomA->getCallFlag() !== $roomB->getCallFlag()) {
 			return $roomA->getCallFlag() !== Participant::FLAG_DISCONNECTED ? -1 : 1;
diff --git a/tests/php/Dashboard/TalkWidgetTest.php b/tests/php/Dashboard/TalkWidgetTest.php
new file mode 100644
index 00000000000..4458ed03a4a
--- /dev/null
+++ b/tests/php/Dashboard/TalkWidgetTest.php
@@ -0,0 +1,131 @@
+<?php
+
+declare(strict_types=1);
+/**
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\Talk\Tests\php\Dashboard;
+
+use OCA\Talk\Chat\ChatManager;
+use OCA\Talk\Chat\MessageParser;
+use OCA\Talk\Config;
+use OCA\Talk\Dashboard\TalkWidget;
+use OCA\Talk\Manager;
+use OCA\Talk\Model\Attendee;
+use OCA\Talk\Model\Message;
+use OCA\Talk\Participant;
+use OCA\Talk\Room;
+use OCA\Talk\Service\AvatarService;
+use OCA\Talk\Service\ParticipantService;
+use OCA\Talk\Service\ProxyCacheMessageService;
+use OCA\Talk\Webinary;
+use OCP\AppFramework\Utility\ITimeFactory;
+use OCP\Comments\IComment;
+use OCP\EventDispatcher\IEventDispatcher;
+use OCP\IL10N;
+use OCP\IURLGenerator;
+use OCP\IUserSession;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\MockObject\MockObject;
+use Test\TestCase;
+
+class TalkWidgetTest extends TestCase {
+	protected Manager&MockObject $manager;
+	protected ParticipantService&MockObject $participantService;
+	protected MessageParser&MockObject $messageParser;
+	protected ChatManager&MockObject $chatManager;
+	protected TalkWidget $widget;
+
+	public function setUp(): void {
+		parent::setUp();
+
+		$l10n = $this->createMock(IL10N::class);
+		$l10n->method('t')->willReturnCallback(static fn (string $text): string => $text);
+
+		$this->manager = $this->createMock(Manager::class);
+		$this->participantService = $this->createMock(ParticipantService::class);
+		$this->messageParser = $this->createMock(MessageParser::class);
+		$this->chatManager = $this->createMock(ChatManager::class);
+
+		$this->widget = new TalkWidget(
+			$this->createMock(IUserSession::class),
+			$this->createMock(Config::class),
+			$this->createMock(IURLGenerator::class),
+			$l10n,
+			$this->manager,
+			$this->createMock(AvatarService::class),
+			$this->participantService,
+			$this->messageParser,
+			$this->chatManager,
+			$this->createMock(ProxyCacheMessageService::class),
+			$this->createMock(IEventDispatcher::class),
+			$this->createMock(ITimeFactory::class),
+		);
+	}
+
+	public static function dataHasUnreadMention(): array {
+		return [
+			'no mention, never read' => [ChatManager::UNREAD_FIRST_MESSAGE, 0, false],
+			'no mention, migrated marker' => [ChatManager::UNREAD_MIGRATION, 0, false],
+			'no mention, nothing read' => [0, 0, false],
+			'no mention, read' => [10, 0, false],
+			'mention, never read' => [ChatManager::UNREAD_FIRST_MESSAGE, 5, true],
+			'mention after the read marker' => [4, 5, true],
+			'mention at the read marker' => [5, 5, false],
+			'mention before the read marker' => [6, 5, false],
+		];
+	}
+
+	#[DataProvider('dataHasUnreadMention')]
+	public function testHasUnreadMention(int $lastRead, int $lastMention, bool $expected): void {
+		$attendee = new Attendee();
+		$attendee->setLastReadMessage($lastRead);
+		$attendee->setLastMentionMessage($lastMention);
+
+		$this->assertSame($expected, self::invokePrivate($this->widget, 'hasUnreadMention', [$attendee]));
+	}
+
+	public function testGetItemsV2UnreadConversationWithoutMention(): void {
+		$comment = $this->createMock(IComment::class);
+
+		$room = $this->createMock(Room::class);
+		$room->method('getObjectType')->willReturn('');
+		$room->method('getLobbyState')->willReturn(Webinary::LOBBY_NONE);
+		$room->method('getCallFlag')->willReturn(Participant::FLAG_DISCONNECTED);
+		$room->method('isFederatedConversation')->willReturn(false);
+		$room->method('getType')->willReturn(Room::TYPE_CHANGELOG);
+		$room->method('getLastMessageId')->willReturn(110);
+		$room->method('getLastMessage')->willReturn($comment);
+		$room->method('getDisplayName')->willReturn('user');
+		$room->method('getToken')->willReturn('token');
+
+		// Never read (-2) and never mentioned (0), as the changelog conversation
+		// of a user who did not open it yet
+		$attendee = new Attendee();
+		$attendee->setActorType(Attendee::ACTOR_USERS);
+		$attendee->setActorId('user');
+		$attendee->setLastReadMessage(ChatManager::UNREAD_FIRST_MESSAGE);
+		$attendee->setLastMentionMessage(0);
+
+		$this->manager->method('getRoomsForUser')->willReturn([$room]);
+		$this->participantService->method('getParticipant')
+			->willReturn(new Participant($room, $attendee, null));
+
+		$message = $this->createMock(Message::class);
+		$message->method('getVisibility')->willReturn(true);
+		$message->method('getMessageParameters')->willReturn([]);
+		$message->method('getMessage')->willReturn('Changelog');
+		$message->method('getExpirationDateTime')->willReturn(null);
+		$this->messageParser->method('createMessage')->willReturn($message);
+
+		// "0" is not a message: asking for it fails with an InvalidArgumentException
+		$this->chatManager->expects($this->never())->method('getComment');
+
+		$items = $this->widget->getItemsV2('user');
+
+		$this->assertCount(1, $items->getItems());
+		$this->assertSame('No unread mentions', $items->getHalfEmptyContentMessage());
+	}
+}