diff --git a/test/form_builder/wrapper_test.rb b/test/form_builder/wrapper_test.rb
index 5958cc3bf..9c7786ee6 100644
--- a/test/form_builder/wrapper_test.rb
+++ b/test/form_builder/wrapper_test.rb
@@ -195,12 +195,12 @@ class WrapperTest < ActionView::TestCase
       with_form_for @user, :name
       assert_no_select "section.custom_wrapper div.another_wrapper label"
       assert_no_select "section.custom_wrapper div.another_wrapper input.string"
-      output_buffer.replace ""
+      output_buffer.to_s.replace ""
 
       with_form_for @user, :name, wrapper: :another
       assert_select "section.custom_wrapper div.another_wrapper label"
       assert_select "section.custom_wrapper div.another_wrapper input.string"
-      output_buffer.replace ""
+      output_buffer.to_s.replace ""
     end
 
     with_form_for @user, :name, wrapper: custom_wrapper