diff --git a/boards/models/tag.py b/boards/models/tag.py
--- a/boards/models/tag.py
+++ b/boards/models/tag.py
@@ -1,6 +1,6 @@
 from boards.models import Thread, Post
 from django.db import models
-from django.db.models import Count
+from django.db.models import Count, Sum
 
 __author__ = 'neko259'
 
@@ -92,8 +92,12 @@ class Tag(models.Model):
     def get_post_count(self, archived=False):
         posts_count = 0
 
-        for thread in self.threads.annotate(Count('replies')).filter(
-                archived=archived):
-            posts_count += thread.replies__count
+        threads = self.threads.filter(archived=archived)
+        if threads.exists():
+            posts_count = threads.annotate(posts_count=Count('replies')).aggregate(
+                posts_sum=Sum('posts_count'))['posts_sum']
+
+        if not posts_count:
+            posts_count = 0
 
         return posts_count