diff --git a/plugins/chat/app/services/chat/list_channel_messages.rb b/plugins/chat/app/services/chat/list_channel_messages.rb
index 6c1f5155a49..affcfabbe07 100644
--- a/plugins/chat/app/services/chat/list_channel_messages.rb
+++ b/plugins/chat/app/services/chat/list_channel_messages.rb
@@ -158,7 +158,9 @@ module Chat
     end
 
     def update_membership_last_viewed_at(guardian:, **)
-      context.membership&.update!(last_viewed_at: Time.zone.now)
+      Scheduler::Defer.later "Chat::ListChannelMessages - defer update_membership_last_viewed_at" do
+        context.membership&.update!(last_viewed_at: Time.zone.now)
+      end
     end
   end
 end
diff --git a/plugins/chat/spec/requests/chat/api/channel_messages_controller_spec.rb b/plugins/chat/spec/requests/chat/api/channel_messages_controller_spec.rb
index d91840d2342..a31ab9e5ce7 100644
--- a/plugins/chat/spec/requests/chat/api/channel_messages_controller_spec.rb
+++ b/plugins/chat/spec/requests/chat/api/channel_messages_controller_spec.rb
@@ -28,6 +28,19 @@ RSpec.describe Chat::Api::ChannelMessagesController do
       end
     end
 
+    context "when readonly mode" do
+      fab!(:message_1) { Fabricate(:chat_message, chat_channel: channel) }
+
+      before { Discourse.enable_readonly_mode }
+      after { Discourse.disable_readonly_mode }
+
+      it "works" do
+        get "/chat/api/channels/#{channel.id}/messages"
+
+        expect(response.status).to eq(200)
+      end
+    end
+
     context "when channnel doesn’t exist" do
       it "returns a 404" do
         get "/chat/api/channels/-999/messages"