diff --git a/boards/models.py b/boards/models.py
--- a/boards/models.py
+++ b/boards/models.py
@@ -139,7 +139,7 @@ class PostManager(models.Manager):
         # must not be shown and be able for replying.
 
         threads = self.get_threads()
-        thread_count = len(threads)
+        thread_count = threads.count()
 
         if thread_count > settings.MAX_THREAD_COUNT:
             num_threads_to_delete = thread_count - settings.MAX_THREAD_COUNT