diff --git a/lib/rbui.rb b/lib/rbui.rb
index e7005576e..63073aeac 100644
--- a/lib/rbui.rb
+++ b/lib/rbui.rb
@@ -6,8 +6,6 @@
 module RBUI
   extend Phlex::Kit
 
-  attr_accessor :namespace
-
   def self.setup
     yield self
     create_namespace_module if namespace
@@ -35,6 +33,14 @@ def self.create_namespace_module
       end
     end
   end
+
+  def self.namespace
+    @namespace ||= nil
+  end
+
+  def self.namespace=(value)
+    @namespace = value
+  end
 end
 
 # Require the Base class first
diff --git a/test/rbui/setup_test.rb b/test/rbui/setup_test.rb
new file mode 100644
index 000000000..8e796121a
--- /dev/null
+++ b/test/rbui/setup_test.rb
@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+require "test_helper"
+
+class RBUI::SetupTest < Minitest::Test
+  def setup
+    @original_namespace = RBUI.namespace
+  end
+
+  def teardown
+    RBUI.namespace = @original_namespace
+    Object.send(:remove_const, :UI) if Object.const_defined?(:UI)
+  end
+
+  def test_default_namespace
+    RBUI.setup {}
+
+    assert_nil RBUI.namespace
+    assert_kind_of RBUI::Base, RBUI::Button.new
+  end
+
+  def test_custom_namespace
+    RBUI.setup do |config|
+      config.namespace = "UI"
+    end
+
+    assert_equal "UI", RBUI.namespace
+    assert_equal RBUI::Base, UI::Base
+    assert_kind_of RBUI::Base, UI::Button.new
+  end
+end