diff --git a/app/blueprints/threads/__init__.py b/app/blueprints/threads/__init__.py
index 3c7039c4..28c52c02 100644
--- a/app/blueprints/threads/__init__.py
+++ b/app/blueprints/threads/__init__.py
@@ -367,7 +367,8 @@ def new():
 				add_notification(mentioned, current_user, NotificationType.NEW_THREAD,
 								 msg, thread.get_view_url(), thread.package)
 
-				thread.watchers.append(mentioned)
+				if mentioned not in thread.watchers:
+					thread.watchers.append(mentioned)
 
 			notif_msg = "New thread '{}'".format(thread.title)
 			if package is not None: