diff --git a/app/models/topic.rb b/app/models/topic.rb
index 95cb1b94dfa..6f155fec2f9 100644
--- a/app/models/topic.rb
+++ b/app/models/topic.rb
@@ -1846,7 +1846,7 @@ end
 #  idx_topics_user_id_deleted_at           (user_id) WHERE (deleted_at IS NULL)
 #  idxtopicslug                            (slug) WHERE ((deleted_at IS NULL) AND (slug IS NOT NULL))
 #  index_topics_on_bannered_until          (bannered_until) WHERE (bannered_until IS NOT NULL)
-#  index_topics_on_bumped_at               (bumped_at)
+#  index_topics_on_bumped_at_public        (bumped_at) WHERE ((deleted_at IS NULL) AND ((archetype)::text <> 'private_message'::text))
 #  index_topics_on_created_at_and_visible  (created_at,visible) WHERE ((deleted_at IS NULL) AND ((archetype)::text <> 'private_message'::text))
 #  index_topics_on_id_and_deleted_at       (id,deleted_at)
 #  index_topics_on_id_filtered_banner      (id) UNIQUE WHERE (((archetype)::text = 'banner'::text) AND (deleted_at IS NULL))
diff --git a/db/post_migrate/20210922064213_alter_bumped_at_indexes_on_topics.rb b/db/post_migrate/20210922064213_alter_bumped_at_indexes_on_topics.rb
new file mode 100644
index 00000000000..037b6c20fc4
--- /dev/null
+++ b/db/post_migrate/20210922064213_alter_bumped_at_indexes_on_topics.rb
@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+class AlterBumpedAtIndexesOnTopics < ActiveRecord::Migration[6.1]
+  disable_ddl_transaction!
+
+  def up
+    execute(<<~SQL)
+    CREATE INDEX CONCURRENTLY IF NOT EXISTS index_topics_on_bumped_at_public
+    ON topics (bumped_at)
+    WHERE ((deleted_at IS NULL) AND ((archetype)::text <> 'private_message'::text));
+    SQL
+
+    execute(<<~SQL)
+    DROP INDEX IF EXISTS index_topics_on_bumped_at;
+    SQL
+
+    # The following index is known to have not been properly renamed. Drop it if
+    # exists just in case.
+    execute(<<~SQL)
+    DROP INDEX IF EXISTS index_forum_threads_on_bumped_at;
+    SQL
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end
diff --git a/lib/topic_query.rb b/lib/topic_query.rb
index 25362ab862f..57ffb9a726d 100644
--- a/lib/topic_query.rb
+++ b/lib/topic_query.rb
@@ -625,11 +625,11 @@ class TopicQuery
     @options[:category_id] = category_id
     if category_id
       if options[:no_subcategories]
-        result = result.where('categories.id = ?', category_id)
+        result = result.where('topics.category_id = ?', category_id)
       else
-        result = result.where("categories.id IN (?)", Category.subcategory_ids(category_id))
+        result = result.where("topics.category_id IN (?)", Category.subcategory_ids(category_id))
         if !SiteSetting.show_category_definitions_in_topic_lists
-          result = result.where("categories.topic_id <> topics.id OR categories.id = ?", category_id)
+          result = result.where("categories.topic_id <> topics.id OR topics.category_id = ?", category_id)
         end
       end
       result = result.references(:categories)
diff --git a/spec/components/topic_query_spec.rb b/spec/components/topic_query_spec.rb
index cd6595733ea..a7e7f2ecc01 100644
--- a/spec/components/topic_query_spec.rb
+++ b/spec/components/topic_query_spec.rb
@@ -268,33 +268,100 @@ describe TopicQuery do
       let!(:subcategory) { Fabricate(:category_with_definition, parent_category_id: category.id) }
       let(:subsubcategory) { Fabricate(:category_with_definition, parent_category_id: subcategory.id) }
 
+      # Not used in assertions but fabricated to ensure we're not leaking topics
+      # across categories
+      let!(:_category) { Fabricate(:category_with_definition) }
+      let!(:_subcategory) { Fabricate(:category_with_definition, parent_category_id: _category.id) }
+
       it "works with subcategories" do
-        expect(TopicQuery.new(moderator, category: category.id).list_latest.topics.size).to eq(1)
-        expect(TopicQuery.new(moderator, category: subcategory.id).list_latest.topics.size).to eq(1)
-        expect(TopicQuery.new(moderator, category: category.id, no_subcategories: true).list_latest.topics.size).to eq(1)
+        expect(
+          TopicQuery
+            .new(moderator, category: category.id)
+            .list_latest.topics
+        ).to contain_exactly(category.topic)
+
+        expect(
+          TopicQuery
+            .new(moderator, category: subcategory.id)
+            .list_latest.topics
+        ).to contain_exactly(subcategory.topic)
+
+        expect(
+          TopicQuery
+            .new(moderator, category: category.id, no_subcategories: true)
+            .list_latest.topics
+        ).to contain_exactly(category.topic)
       end
 
       it "shows a subcategory definition topic in its parent list with the right site setting" do
         SiteSetting.show_category_definitions_in_topic_lists = true
-        expect(TopicQuery.new(moderator, category: category.id).list_latest.topics.size).to eq(2)
+
+        expect(
+          TopicQuery
+            .new(moderator, category: category.id)
+            .list_latest.topics
+        ).to contain_exactly(category.topic, subcategory.topic)
       end
 
       it "works with subsubcategories" do
         SiteSetting.max_category_nesting = 3
 
-        Fabricate(:topic, category: category)
-        Fabricate(:topic, category: subcategory)
-        Fabricate(:topic, category: subsubcategory)
+        category_topic = Fabricate(:topic, category: category)
+        subcategory_topic = Fabricate(:topic, category: subcategory)
+        subsubcategory_topic = Fabricate(:topic, category: subsubcategory)
 
         SiteSetting.max_category_nesting = 2
-        expect(TopicQuery.new(moderator, category: category.id).list_latest.topics.size).to eq(3)
-        expect(TopicQuery.new(moderator, category: subcategory.id).list_latest.topics.size).to eq(3)
-        expect(TopicQuery.new(moderator, category: subsubcategory.id).list_latest.topics.size).to eq(2)
+
+        expect(
+          TopicQuery
+            .new(moderator, category: category.id)
+            .list_latest.topics
+        ).to contain_exactly(category.topic, category_topic, subcategory_topic)
+
+        expect(
+          TopicQuery
+            .new(moderator, category: subcategory.id)
+            .list_latest.topics
+        ).to contain_exactly(
+          subcategory.topic,
+          subcategory_topic,
+          subsubcategory_topic
+        )
+
+        expect(
+          TopicQuery
+            .new(moderator, category: subsubcategory.id)
+            .list_latest.topics
+        ).to contain_exactly(subsubcategory.topic, subsubcategory_topic)
 
         SiteSetting.max_category_nesting = 3
-        expect(TopicQuery.new(moderator, category: category.id).list_latest.topics.size).to eq(4)
-        expect(TopicQuery.new(moderator, category: subcategory.id).list_latest.topics.size).to eq(3)
-        expect(TopicQuery.new(moderator, category: subsubcategory.id).list_latest.topics.size).to eq(2)
+
+        expect(
+          TopicQuery
+            .new(moderator, category: category.id)
+            .list_latest.topics
+        ).to contain_exactly(
+          category.topic,
+          category_topic,
+          subcategory_topic,
+          subsubcategory_topic
+        )
+
+        expect(
+          TopicQuery
+            .new(moderator, category: subcategory.id)
+            .list_latest.topics
+        ).to contain_exactly(
+          subcategory.topic,
+          subcategory_topic,
+          subsubcategory_topic
+        )
+
+        expect(
+          TopicQuery
+            .new(moderator, category: subsubcategory.id)
+            .list_latest.topics
+        ).to contain_exactly(subsubcategory.topic, subsubcategory_topic)
       end
     end
   end