diff --git a/app/serializers/user_bookmark_serializer.rb b/app/serializers/user_bookmark_serializer.rb
index d408878adf..1edb26adb6 100644
--- a/app/serializers/user_bookmark_serializer.rb
+++ b/app/serializers/user_bookmark_serializer.rb
@@ -109,7 +109,24 @@ class UserBookmarkSerializer < ApplicationSerializer
   end
 
   def cooked
-    post.cooked
+    @cooked ||= \
+      if object.for_topic && last_read_post_number.present?
+        for_topic_cooked_post
+      else
+        post.cooked
+      end
+  end
+
+  def for_topic_cooked_post
+    post_number = [last_read_post_number + 1, highest_post_number].min
+    posts = Post.where(topic: topic, post_type: Post.types[:regular]).order(:post_number)
+    first_unread_cooked = posts.where("post_number >= ?", post_number).pluck_first(:cooked)
+
+    # if first_unread_cooked is blank this likely means that the last
+    # read post was either deleted or is a small action post.
+    # in this case we should just get the last regular post and
+    # use that for the cooked value so we have something to show
+    first_unread_cooked || posts.last.cooked
   end
 
   def slug
diff --git a/spec/serializers/user_bookmark_serializer_spec.rb b/spec/serializers/user_bookmark_serializer_spec.rb
index 8376c98cd3..41ac72fd17 100644
--- a/spec/serializers/user_bookmark_serializer_spec.rb
+++ b/spec/serializers/user_bookmark_serializer_spec.rb
@@ -30,6 +30,7 @@ RSpec.describe UserBookmarkSerializer do
     expect(s.post_user_username).to eq(bookmark.post.user.username)
     expect(s.post_user_name).to eq(bookmark.post.user.name)
     expect(s.post_user_avatar_template).not_to eq(nil)
+    expect(s.excerpt).to eq(PrettyText.excerpt(post.cooked, 300, keep_emoji_images: true))
   end
 
   it "uses the correct highest_post_number column based on whether the user is staff" do
@@ -45,4 +46,39 @@ RSpec.describe UserBookmarkSerializer do
 
     expect(serializer.highest_post_number).to eq(4)
   end
+
+  context "for_topic bookmarks" do
+    before do
+      bookmark.update!(for_topic: true)
+    end
+
+    it "uses the last_read_post_number + 1 for the for_topic bookmarks excerpt" do
+      next_unread_post = Fabricate(:post_with_long_raw_content, topic: bookmark.topic)
+      Fabricate(:post_with_external_links, topic: bookmark.topic)
+      bookmark.reload
+      TopicUser.change(user.id, bookmark.topic.id, { last_read_post_number: post.post_number })
+      serializer = UserBookmarkSerializer.new(bookmark, scope: Guardian.new(user))
+      expect(serializer.excerpt).to eq(PrettyText.excerpt(next_unread_post.cooked, 300, keep_emoji_images: true))
+    end
+
+    it "does not use a small post for the last unread cooked post" do
+      small_action_post = Fabricate(:small_action, topic: bookmark.topic)
+      next_unread_post = Fabricate(:post_with_long_raw_content, topic: bookmark.topic)
+      Fabricate(:post_with_external_links, topic: bookmark.topic)
+      bookmark.reload
+      TopicUser.change(user.id, bookmark.topic.id, { last_read_post_number: post.post_number })
+      serializer = UserBookmarkSerializer.new(bookmark, scope: Guardian.new(user))
+      expect(serializer.excerpt).to eq(PrettyText.excerpt(next_unread_post.cooked, 300, keep_emoji_images: true))
+    end
+
+    it "handles the last read post in the topic being a small post by getting the last read regular post" do
+      last_regular_post = Fabricate(:post_with_long_raw_content, topic: bookmark.topic)
+      small_action_post = Fabricate(:small_action, topic: bookmark.topic)
+      bookmark.reload
+      TopicUser.change(user.id, bookmark.topic.id, { last_read_post_number: small_action_post.post_number })
+      serializer = UserBookmarkSerializer.new(bookmark, scope: Guardian.new(user))
+      expect(serializer.cooked).to eq(last_regular_post.cooked)
+      expect(serializer.excerpt).to eq(PrettyText.excerpt(last_regular_post.cooked, 300, keep_emoji_images: true))
+    end
+  end
 end