diff --git a/app/controllers/messages_controller.rb b/app/controllers/messages_controller.rb
index 71c2107f3..252d6645c 100644
--- a/app/controllers/messages_controller.rb
+++ b/app/controllers/messages_controller.rb
@@ -15,6 +15,8 @@ class MessagesController < ApplicationController
     else
       redirect_to chat_path(@chat), alert: @message.errors.full_messages.to_sentence
     end
+  rescue ActiveRecord::InvalidForeignKey
+    redirect_to chats_path, alert: t(".chat_not_found")
   end
 
   # Called by the chat watchdog when an assistant "Thinking…" bubble has waited
diff --git a/config/locales/views/messages/en.yml b/config/locales/views/messages/en.yml
index dee376568..c0c6603ed 100644
--- a/config/locales/views/messages/en.yml
+++ b/config/locales/views/messages/en.yml
@@ -1,6 +1,8 @@
 ---
 en:
   messages:
+    create:
+      chat_not_found: This chat is no longer available.
     chat_form:
       placeholder: "Ask anything ..."
       disclaimer: "AI responses are informational only. Not financial advice!"
diff --git a/test/controllers/messages_controller_test.rb b/test/controllers/messages_controller_test.rb
index d97fd3f96..6fdc425a4 100644
--- a/test/controllers/messages_controller_test.rb
+++ b/test/controllers/messages_controller_test.rb
@@ -12,6 +12,15 @@ class MessagesControllerTest < ActionDispatch::IntegrationTest
     assert_redirected_to chat_path(@chat, thinking: true)
   end
 
+  test "redirects to chats when message save races with chat deletion" do
+    UserMessage.any_instance.stubs(:save).raises(ActiveRecord::InvalidForeignKey)
+
+    post chat_messages_url(@chat), params: { message: { content: "Hello", ai_model: "gpt-4.1" } }
+
+    assert_redirected_to chats_path
+    assert_equal I18n.t("messages.create.chat_not_found"), flash[:alert]
+  end
+
   test "cannot create a message if AI is disabled" do
     @user.update!(ai_enabled: false)