diff --git a/app/models/category_list.rb b/app/models/category_list.rb
index fd3d892312..712adab190 100644
--- a/app/models/category_list.rb
+++ b/app/models/category_list.rb
@@ -103,7 +103,8 @@ class CategoryList
         @categories.insert(insert_at || @categories.size, uncategorized)
       end
 
-      if @all_topics.present? && uncategorized.present?
+      if uncategorized.present?
+        @all_topics ||= []
         uncategorized.displayable_topics = uncategorized_topics
         @all_topics << uncategorized_topics
         @all_topics.flatten!
diff --git a/spec/components/category_list_spec.rb b/spec/components/category_list_spec.rb
index 537788a3dd..e561df9f25 100644
--- a/spec/components/category_list_spec.rb
+++ b/spec/components/category_list_spec.rb
@@ -22,6 +22,7 @@ describe CategoryList do
         category.slug.should == SiteSetting.uncategorized_name
         category.topics_week.should == 1
         category.featured_topics.should == [topic]
+        category.displayable_topics.should == [topic] # CategoryDetailedSerializer needs this attribute
       end
 
       it 'does not return an invisible topic' do