diff --git a/app/models/assistant/slug.rb b/app/models/assistant/slug.rb
index cc56eb19..876620ac 100644
--- a/app/models/assistant/slug.rb
+++ b/app/models/assistant/slug.rb
@@ -4,6 +4,7 @@ module Assistant::Slug
   included do
     before_validation :set_default_slug
     before_validation :clear_conflicting_deleted_assistant_slug
+    validates :slug, uniqueness: { scope: :user_id, message: "has already been taken" }
   end
 
   private
diff --git a/test/controllers/settings/assistants_controller_test.rb b/test/controllers/settings/assistants_controller_test.rb
index dd2735fe..2db8a531 100644
--- a/test/controllers/settings/assistants_controller_test.rb
+++ b/test/controllers/settings/assistants_controller_test.rb
@@ -24,6 +24,24 @@ class Settings::AssistantsControllerTest < ActionDispatch::IntegrationTest
     assert_equal params, Assistant.last.slice(:name, :description, :instructions, :language_model_id)
   end
 
+  test "should show error when creating assistant with duplicate slug" do
+    existing_assistant = assistants(:samantha)
+    params = {
+      name: "New Assistant",
+      slug: existing_assistant.slug,
+      description: "A new description",
+      instructions: "New instructions",
+      language_model_id: language_models(:gpt_4o).id
+    }
+
+    assert_no_difference("Assistant.count") do
+      post settings_assistants_url, params: { assistant: params }
+    end
+
+    assert_response :unprocessable_entity
+    assert_contains_text "main", "Slug has already been taken"
+  end
+
   test "should get edit" do
     get edit_settings_assistant_url(@assistant)
     assert_response :success