diff --git a/lib/Chat/Parser/UserMention.php b/lib/Chat/Parser/UserMention.php
index 377eb1aefea..e5f17c4d418 100644
--- a/lib/Chat/Parser/UserMention.php
+++ b/lib/Chat/Parser/UserMention.php
@@ -94,7 +94,14 @@ protected function parseMessage(Message $chatMessage): void {
 
 		$mentionTypeCount = [];
 
+		// Set the current message as comment content, so that the message finds
+		// mentions which are now part of the message, but were not on the original
+		// comment, e.g. mentions at the beginning of captions
+		$originalCommentMessage = $comment->getMessage();
+		$comment->setMessage($message, ChatManager::MAX_CHAT_LENGTH + 10000);
 		$mentions = $comment->getMentions();
+		$comment->setMessage($originalCommentMessage, ChatManager::MAX_CHAT_LENGTH);
+
 		// TODO This can be removed once getMentions() returns sorted results (Nextcloud 21+)
 		usort($mentions, static function (array $m1, array $m2) {
 			return mb_strlen($m2['id']) <=> mb_strlen($m1['id']);
diff --git a/tests/integration/features/chat/file-share.feature b/tests/integration/features/chat/file-share.feature
index 54c5c7d3660..96f4237ee57 100644
--- a/tests/integration/features/chat/file-share.feature
+++ b/tests/integration/features/chat/file-share.feature
@@ -32,6 +32,16 @@ Feature: chat/file-share
       | room        | actorType | actorId      | actorDisplayName         | message                                                           | messageParameters |
       | public room | users     | participant1 | participant1-displayname | Hello {mention-user1} this is a caption for the attached document | "IGNORE"          |
 
+  Scenario: Share a file with caption that only is a mention
+    Given user "participant1" creates room "public room" (v4)
+      | roomType | 3 |
+      | roomName | room |
+    When user "participant1" shares "welcome.txt" with room "public room"
+      | talkMetaData | {"caption":"@participant2"} |
+    Then user "participant1" sees the following messages in room "public room" with 200
+      | room        | actorType | actorId      | actorDisplayName         | message         | messageParameters |
+      | public room | users     | participant1 | participant1-displayname | {mention-user1} | "IGNORE"          |
+
   Scenario: Can not share a file without chat permission
     Given user "participant1" creates room "public room" (v4)
       | roomType | 3 |