diff --git a/test/unit/comment_test.rb b/test/unit/comment_test.rb
index c0ce7ec..f845e52 100644
--- a/test/unit/comment_test.rb
+++ b/test/unit/comment_test.rb
@@ -301,6 +301,19 @@ class CommentTest < ActiveSupport::TestCase
     assert result[1].replies.empty?
   end
 
+  should "return activities comments when some comment on thread is spam" do
+    person = fast_create(Person)
+    a = TextileArticle.create!(:profile => person, :name => 'My article', :body => 'Article body')
+    c0 = Comment.create(:source => a, :body => 'Root comment', :author => person)
+    c1 = Comment.create(:reply_of_id => c0.id, :source => a, :body => 'c1', :author => person)
+    spam = Comment.create(:spam => true, :reply_of_id => c0.id, :source => a, :body => 'spam', :author => person)
+    c2 = Comment.create(:reply_of_id => spam.id, :source => a, :body => 'c2', :author => person)
+    result = a.activity.comments_as_thread
+    assert_equal c0, result[0]
+    assert_equal [c1], result[0].replies
+    assert_equal c2, result[1]
+  end
+
   should 'provide author url for authenticated user' do
     author = Person.new
     author.expects(:url).returns('http://blabla.net/author')
diff --git a/vendor/plugins/action_tracker_has_comments/init.rb b/vendor/plugins/action_tracker_has_comments/init.rb
index e5a7abf..2f0375e 100644
--- a/vendor/plugins/action_tracker_has_comments/init.rb
+++ b/vendor/plugins/action_tracker_has_comments/init.rb
@@ -16,7 +16,13 @@ Rails.configuration.to_prepare do
       self.comments.each do |c|
         c.replies = []
         result[c.id] ||= c
-        c.reply_of_id.nil? ? root << c : result[c.reply_of_id].replies << c
+        if c.reply_of_id.nil?
+          root << c
+        elsif result[c.reply_of_id]
+          result[c.reply_of_id].replies << c
+        else # Comment is a reply but the reply is not being displayed - is spam, for example
+          root << c
+        end
       end
       root
     end
--
libgit2 0.21.2