diff --git a/test/irb/test_completion.rb b/test/irb/test_completion.rb
index a661d68c59..1fd42999c6 100644
--- a/test/irb/test_completion.rb
+++ b/test/irb/test_completion.rb
@@ -88,6 +88,7 @@ module TestIRB
       str_example = ''
       assert_include(IRB::InputCompletor.retrieve_completion_data("str_examp", bind: binding), "str_example")
       assert_equal(IRB::InputCompletor.retrieve_completion_data("str_example", bind: binding, doc_namespace: true), "String")
+      assert_equal(IRB::InputCompletor.retrieve_completion_data("str_example.to_s", bind: binding, doc_namespace: true), "String.to_s")
     end
 
     def test_complete_class_method