diff --git a/ext/tk/lib/multi-tk.rb b/ext/tk/lib/multi-tk.rb
index e054f3dd91..48e652e882 100644
--- a/ext/tk/lib/multi-tk.rb
+++ b/ext/tk/lib/multi-tk.rb
@@ -27,7 +27,7 @@ MultiTkIp_OK.freeze
 class MultiTkIp
 
   # ignore exception on the mainloop
-  TclTkLib.mainloop_abort_on_exception = false
+  TclTkLib.mainloop_abort_on_exception = nil
 
   ######################################