diff --git a/app/models/forum.py b/app/models/forum.py
index c459375..71d2381 100644
--- a/app/models/forum.py
+++ b/app/models/forum.py
@@ -37,4 +37,4 @@ class Forum(db.Model):
 
     def post_count(self):
         """Number of posts in every topic of the forum, without subforums."""
-        return sum(len(thread.comments) for thread in self.topics)
+        return sum(len(t.thread.comments) for t in self.topics)