diff --git a/test/irb/test_cmd.rb b/test/irb/test_cmd.rb
index c2e8cc1774..bcfb1d0b86 100644
--- a/test/irb/test_cmd.rb
+++ b/test/irb/test_cmd.rb
@@ -523,7 +523,7 @@ module TestIRB
         def show_source_test_method
           unless true
           end
-        end
+        end unless defined?(show_source_test_method)
       EOS
 
       out, err = execute_lines(