diff --git a/boards/models.py b/boards/models.py
--- a/boards/models.py
+++ b/boards/models.py
@@ -66,6 +66,13 @@ class PostManager(models.Manager):
     def delete_post(self, post):
         if post.replies.count() > 0:
             map(self.delete_post, post.replies.all())
+
+        # Update thread's last edit time (used as cache key)
+        thread = post.thread
+        if thread:
+            thread.last_edit_time = timezone.now()
+            thread.save()
+
         post.delete()
 
     def delete_posts_by_ip(self, ip):