diff --git a/plugins/chat/app/services/update_user_last_read.rb b/plugins/chat/app/services/update_user_last_read.rb
index 45b0a33050c..ad9e90dc6ca 100644
--- a/plugins/chat/app/services/update_user_last_read.rb
+++ b/plugins/chat/app/services/update_user_last_read.rb
@@ -17,9 +17,9 @@ module Chat
       #   @param [Guardian] guardian
       #   @return [Chat::Service::Base::Context]
 
+      contract
       model :membership, :fetch_active_membership
       policy :invalid_access
-      contract
       policy :ensure_message_id_recency
       policy :ensure_message_exists
       step :update_last_read_message_id
@@ -31,6 +31,8 @@ module Chat
         attribute :message_id, :integer
         attribute :user_id, :integer
         attribute :channel_id, :integer
+
+        validates :message_id, :user_id, :channel_id, presence: true
       end
 
       private
diff --git a/plugins/chat/spec/services/update_user_last_read_spec.rb b/plugins/chat/spec/services/update_user_last_read_spec.rb
index 4926e824f6c..40a5b105605 100644
--- a/plugins/chat/spec/services/update_user_last_read_spec.rb
+++ b/plugins/chat/spec/services/update_user_last_read_spec.rb
@@ -1,118 +1,119 @@
 # frozen_string_literal: true
 
-RSpec.describe(Chat::Service::UpdateUserLastRead) do
-  subject(:result) { described_class.call(params) }
-
-  fab!(:current_user) { Fabricate(:user) }
-  fab!(:channel) { Fabricate(:chat_channel) }
-  fab!(:membership) do
-    Fabricate(:user_chat_channel_membership, user: current_user, chat_channel: channel)
-  end
-  fab!(:message_1) { Fabricate(:chat_message, chat_channel: membership.chat_channel) }
-
-  let(:guardian) { Guardian.new(current_user) }
-  let(:params) do
-    {
-      guardian: guardian,
-      user_id: current_user.id,
-      channel_id: channel.id,
-      message_id: message_1.id,
-    }
+RSpec.describe Chat::Service::UpdateUserLastRead do
+  describe Chat::Service::UpdateUserLastRead::Contract, type: :model do
+    it { is_expected.to validate_presence_of :user_id }
+    it { is_expected.to validate_presence_of :channel_id }
+    it { is_expected.to validate_presence_of :message_id }
   end
 
-  context "when channel_id is not provided" do
-    before { params.delete(:channel_id) }
+  describe ".call" do
+    subject(:result) { described_class.call(params) }
 
-    it { is_expected.to fail_to_find_a_model(:membership) }
-  end
-
-  context "when user_id is not provided" do
-    before { params.delete(:user_id) }
-
-    it { is_expected.to fail_to_find_a_model(:membership) }
-  end
-
-  context "when user has no membership" do
-    before { membership.destroy! }
-
-    it { is_expected.to fail_to_find_a_model(:membership) }
-  end
-
-  context "when user can’t access the channel" do
+    fab!(:current_user) { Fabricate(:user) }
+    fab!(:channel) { Fabricate(:chat_channel) }
     fab!(:membership) do
-      Fabricate(
-        :user_chat_channel_membership,
-        user: current_user,
-        chat_channel: Fabricate(:private_category_channel),
-      )
+      Fabricate(:user_chat_channel_membership, user: current_user, chat_channel: channel)
+    end
+    fab!(:message_1) { Fabricate(:chat_message, chat_channel: membership.chat_channel) }
+
+    let(:guardian) { Guardian.new(current_user) }
+    let(:params) do
+      {
+        guardian: guardian,
+        user_id: current_user.id,
+        channel_id: channel.id,
+        message_id: message_1.id,
+      }
     end
 
-    before { params[:channel_id] = membership.chat_channel.id }
+    context "when params are not valid" do
+      before { params.delete(:user_id) }
 
-    it { is_expected.to fail_a_policy(:invalid_access) }
-  end
-
-  context "when message_id is older than membership's last_read_message_id" do
-    before do
-      params[:message_id] = -2
-      membership.update!(last_read_message_id: -1)
+      it { is_expected.to fail_a_contract }
     end
 
-    it { is_expected.to fail_a_policy(:ensure_message_id_recency) }
-  end
+    context "when params are valid" do
+      context "when user has no membership" do
+        before { membership.destroy! }
 
-  context "when message doesn’t exist" do
-    before do
-      params[:message_id] = 2
-      membership.update!(last_read_message_id: 1)
-    end
+        it { is_expected.to fail_to_find_a_model(:membership) }
+      end
 
-    it { is_expected.to fail_a_policy(:ensure_message_exists) }
-  end
+      context "when user can’t access the channel" do
+        fab!(:membership) do
+          Fabricate(
+            :user_chat_channel_membership,
+            user: current_user,
+            chat_channel: Fabricate(:private_category_channel),
+          )
+        end
 
-  context "when params are valid" do
-    before { Jobs.run_immediately! }
+        before { params[:channel_id] = membership.chat_channel.id }
 
-    it "sets the service result as successful" do
-      expect(result).to be_a_success
-    end
+        it { is_expected.to fail_a_policy(:invalid_access) }
+      end
 
-    it "updates the last_read message id" do
-      expect { result }.to change { membership.reload.last_read_message_id }.to(message_1.id)
-    end
+      context "when message_id is older than membership's last_read_message_id" do
+        before do
+          params[:message_id] = -2
+          membership.update!(last_read_message_id: -1)
+        end
 
-    it "marks existing notifications related to the message as read" do
-      expect {
-        notification =
+        it { is_expected.to fail_a_policy(:ensure_message_id_recency) }
+      end
+
+      context "when message doesn’t exist" do
+        before do
+          params[:message_id] = 2
+          membership.update!(last_read_message_id: 1)
+        end
+
+        it { is_expected.to fail_a_policy(:ensure_message_exists) }
+      end
+
+      context "when everything is fine" do
+        fab!(:notification) do
           Fabricate(
             :notification,
             notification_type: Notification.types[:chat_mention],
             user: current_user,
           )
+        end
 
-        # FIXME: we need a better way to create proper chat mention
-        ChatMention.create!(notification: notification, user: current_user, chat_message: message_1)
-      }.to change {
-        Notification.where(
-          notification_type: Notification.types[:chat_mention],
-          user: current_user,
-          read: false,
-        ).count
-      }.by(1)
+        let(:messages) { MessageBus.track_publish { result } }
 
-      expect { result }.to change {
-        Notification.where(
-          notification_type: Notification.types[:chat_mention],
-          user: current_user,
-          read: false,
-        ).count
-      }.by(-1)
-    end
+        before do
+          Jobs.run_immediately!
+          ChatMention.create!(
+            notification: notification,
+            user: current_user,
+            chat_message: message_1,
+          )
+        end
 
-    it "publishes new last read to clients" do
-      messages = MessageBus.track_publish { result }
+        it "sets the service result as successful" do
+          expect(result).to be_a_success
+        end
 
-      expect(messages.map(&:channel)).to include("/chat/user-tracking-state/#{current_user.id}")
+        it "updates the last_read message id" do
+          expect { result }.to change { membership.reload.last_read_message_id }.to(message_1.id)
+        end
+
+        it "marks existing notifications related to the message as read" do
+          expect { result }.to change {
+            Notification.where(
+              notification_type: Notification.types[:chat_mention],
+              user: current_user,
+              read: false,
+            ).count
+          }.by(-1)
+        end
+
+        it "publishes new last read to clients" do
+          expect(messages.map(&:channel)).to include("/chat/user-tracking-state/#{current_user.id}")
+        end
+      end
     end
   end
 end