diff --git a/lib/tkextlib/tcllib/tooltip.rb b/lib/tkextlib/tcllib/tooltip.rb
index 56e2d2cb..cbafd536 100644
--- a/lib/tkextlib/tcllib/tooltip.rb
+++ b/lib/tkextlib/tcllib/tooltip.rb
@@ -33,6 +33,7 @@ def self.package_version
 
 module Tk::Tcllib::Tooltip
   extend TkCore
+  include Tk
 
   WidgetClassName = 'Tooltip'.freeze
   WidgetClassNames[WidgetClassName] ||= self