diff --git a/packages/zammad-addon-bridge/src/app/controllers/channels_cdr_signal_controller.rb b/packages/zammad-addon-bridge/src/app/controllers/channels_cdr_signal_controller.rb
index 409eac7..6446ba2 100644
--- a/packages/zammad-addon-bridge/src/app/controllers/channels_cdr_signal_controller.rb
+++ b/packages/zammad-addon-bridge/src/app/controllers/channels_cdr_signal_controller.rb
@@ -374,6 +374,24 @@ class ChannelsCdrSignalController < ApplicationController
       return
     end
 
+    # Idempotency check: if chat_id is already a group ID, don't overwrite it
+    # This prevents race conditions where multiple group_created webhooks arrive
+    # (e.g., due to retries after API timeouts during group creation)
+    existing_chat_id = ticket.preferences&.dig(:cdr_signal, :chat_id) ||
+                       ticket.preferences&.dig('cdr_signal', 'chat_id')
+    if existing_chat_id&.start_with?('group.')
+      Rails.logger.info "Signal group update: Ticket #{ticket.id} already has group #{existing_chat_id}, ignoring new group #{params[:group_id]}"
+      render json: {
+        success: true,
+        skipped: true,
+        reason: 'Ticket already has a group assigned',
+        existing_group_id: existing_chat_id,
+        ticket_id: ticket.id,
+        ticket_number: ticket.number
+      }, status: :ok
+      return
+    end
+
     # Update ticket preferences with the group information
     ticket.preferences ||= {}
     ticket.preferences[:cdr_signal] ||= {}