diff --git a/plugin.rb b/plugin.rb
index e9866cd..15763e5 100644
--- a/plugin.rb
+++ b/plugin.rb
@@ -188,12 +188,24 @@ after_initialize do
 
   BookmarkQuery.on_preload do |bookmarks, bookmark_query|
     if SiteSetting.assign_enabled?
-      topics = bookmarks.map(&:topic)
-      assignments = Assignment.strict_loading.where(topic_id: topics).includes(:assigned_to).index_by(&:topic_id)
+      if SiteSetting.use_polymorphic_bookmarks
+        topics = Bookmark.select_type(bookmarks, "Topic").map(&:bookmarkable).concat(
+          Bookmark.select_type(bookmarks, "Post").map { |bm| bm.bookmarkable.topic }
+        ).uniq
+        assignments = Assignment.strict_loading.where(topic_id: topics).includes(:assigned_to).index_by(&:topic_id)
 
-      topics.each do |topic|
-        assigned_to = assignments[topic.id]&.assigned_to
-        topic.preload_assigned_to(assigned_to)
+        topics.each do |topic|
+          assigned_to = assignments[topic.id]&.assigned_to
+          topic.preload_assigned_to(assigned_to)
+        end
+      else
+        topics = bookmarks.map(&:topic)
+        assignments = Assignment.strict_loading.where(topic_id: topics).includes(:assigned_to).index_by(&:topic_id)
+
+        topics.each do |topic|
+          assigned_to = assignments[topic.id]&.assigned_to
+          topic.preload_assigned_to(assigned_to)
+        end
       end
     end
   end
@@ -594,6 +606,49 @@ after_initialize do
     BasicUserSerializer.new(topic.assigned_to, scope: scope, root: false).as_json
   end
 
+  add_to_serializer(:user_bookmark, 'include_assigned_to_user?') do
+    (SiteSetting.assigns_public || scope.can_assign?) && topic.assigned_to&.is_a?(User)
+  end
+
+  add_to_serializer(:user_bookmark, :assigned_to_group, false) do
+    BasicGroupSerializer.new(topic.assigned_to, scope: scope, root: false).as_json
+  end
+
+  add_to_serializer(:user_bookmark, 'include_assigned_to_group?') do
+    (SiteSetting.assigns_public || scope.can_assign?) && topic.assigned_to&.is_a?(Group)
+  end
+
+  if SiteSetting.use_polymorphic_bookmarks
+    # UserBookmarkBaseSerializer
+    add_to_class(:user_bookmark_base_serializer, :assigned_to) do
+      @assigned_to ||= bookmarkable_type == "Topic" ? bookmarkable.assigned_to : bookmarkable.topic.assigned_to
+    end
+
+    add_to_class(:user_bookmark_base_serializer, :can_have_assignment?) do
+      ["Post", "Topic"].include?(bookmarkable_type)
+    end
+
+    add_to_serializer(:user_bookmark_base, :assigned_to_user, false) do
+      return if !can_have_assignment?
+      BasicUserSerializer.new(assigned_to, scope: scope, root: false).as_json
+    end
+
+    add_to_serializer(:user_bookmark_base, 'include_assigned_to_user?') do
+      return false if !can_have_assignment?
+      (SiteSetting.assigns_public || scope.can_assign?) && assigned_to&.is_a?(User)
+    end
+
+    add_to_serializer(:user_bookmark_base, :assigned_to_group, false) do
+      return if !can_have_assignment?
+      BasicGroupSerializer.new(assigned_to, scope: scope, root: false).as_json
+    end
+
+    add_to_serializer(:user_bookmark_base, 'include_assigned_to_group?') do
+      return false if !can_have_assignment?
+      (SiteSetting.assigns_public || scope.can_assign?) && assigned_to&.is_a?(Group)
+    end
+  end
+
   add_to_serializer(:basic_user, :assign_icon) do
     'user-plus'
   end
@@ -610,18 +665,6 @@ after_initialize do
     "/g/#{object.name}/assigned/everyone"
   end
 
-  add_to_serializer(:user_bookmark, 'include_assigned_to_user?') do
-    (SiteSetting.assigns_public || scope.can_assign?) && topic.assigned_to&.is_a?(User)
-  end
-
-  add_to_serializer(:user_bookmark, :assigned_to_group, false) do
-    BasicGroupSerializer.new(topic.assigned_to, scope: scope, root: false).as_json
-  end
-
-  add_to_serializer(:user_bookmark, 'include_assigned_to_group?') do
-    (SiteSetting.assigns_public || scope.can_assign?) && topic.assigned_to&.is_a?(Group)
-  end
-
   # PostSerializer
   add_to_serializer(:post, :assigned_to_user) do
     BasicUserSerializer.new(object.assignment.assigned_to, scope: scope, root: false).as_json
diff --git a/spec/serializers/user_bookmark_base_serializer_spec.rb b/spec/serializers/user_bookmark_base_serializer_spec.rb
new file mode 100644
index 0000000..e223377
--- /dev/null
+++ b/spec/serializers/user_bookmark_base_serializer_spec.rb
@@ -0,0 +1,65 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+require_relative '../support/assign_allowed_group'
+
+describe UserBookmarkBaseSerializer do
+  include_context 'A group that is allowed to assign'
+
+  before do
+    SiteSetting.use_polymorphic_bookmarks = true
+    SiteSetting.assign_enabled = true
+    add_to_assign_allowed_group(user)
+  end
+
+  fab!(:user) { Fabricate(:user) }
+  fab!(:topic) { Fabricate(:topic) }
+  fab!(:post) { Fabricate(:post, topic: topic) }
+  let(:guardian) { Guardian.new(user) }
+
+  context "for Topic bookmarkable" do
+    let!(:bookmark) { Fabricate(:bookmark, user: user, bookmarkable: post.topic) }
+    xit "includes assigned user in serializer" do
+      Assigner.new(topic, user).assign(user)
+      serializer = UserTopicBookmarkSerializer.new(bookmark, scope: guardian)
+      bookmark = serializer.as_json[:user_topic_bookmark]
+
+      expect(bookmark[:assigned_to_user][:id]).to eq(user.id)
+      expect(bookmark[:assigned_to_user][:assign_icon]).to eq("user-plus")
+      expect(bookmark[:assigned_to_group]).to be(nil)
+    end
+
+    xit "includes assigned group in serializer" do
+      Assigner.new(topic, user).assign(assign_allowed_group)
+      serializer = UserTopicBookmarkSerializer.new(bookmark, scope: guardian)
+      bookmark = serializer.as_json[:user_topic_bookmark]
+
+      expect(bookmark[:assigned_to_group][:id]).to eq(assign_allowed_group.id)
+      expect(bookmark[:assigned_to_group][:assign_icon]).to eq("group-plus")
+      expect(bookmark[:assigned_to_user]).to be(nil)
+    end
+  end
+
+  context "for Post bookmarkable" do
+    let!(:bookmark) { Fabricate(:bookmark, user: user, bookmarkable: post) }
+    xit "includes assigned user in serializer" do
+      Assigner.new(topic, user).assign(user)
+      serializer = UserPostBookmarkSerializer.new(bookmark, scope: guardian)
+      bookmark = serializer.as_json[:user_post_bookmark]
+
+      expect(bookmark[:assigned_to_user][:id]).to eq(user.id)
+      expect(bookmark[:assigned_to_user][:assign_icon]).to eq("user-plus")
+      expect(bookmark[:assigned_to_group]).to be(nil)
+    end
+
+    xit "includes assigned group in serializer" do
+      Assigner.new(topic, user).assign(assign_allowed_group)
+      serializer = UserPostBookmarkSerializer.new(bookmark, scope: guardian)
+      bookmark = serializer.as_json[:user_post_bookmark]
+
+      expect(bookmark[:assigned_to_group][:id]).to eq(assign_allowed_group.id)
+      expect(bookmark[:assigned_to_group][:assign_icon]).to eq("group-plus")
+      expect(bookmark[:assigned_to_user]).to be(nil)
+    end
+  end
+end