diff --git a/gateway/platforms/mattermost.py b/gateway/platforms/mattermost.py
index 7c9c2d29bac..0e689bed9c5 100644
--- a/gateway/platforms/mattermost.py
+++ b/gateway/platforms/mattermost.py
@@ -661,6 +661,8 @@ class MattermostAdapter(BasePlatformAdapter):
         msg_type = MessageType.TEXT
         if message_text.startswith("/"):
             msg_type = MessageType.COMMAND
+        elif file_ids:
+            msg_type = MessageType.DOCUMENT
 
         # Download file attachments immediately (URLs require auth headers
         # that downstream tools won't have).